diff --git a/UPGRADE.md b/UPGRADE.md
index 84e864e4000..4b39948eca7 100644
--- a/UPGRADE.md
+++ b/UPGRADE.md
@@ -8,6 +8,10 @@ awareness about deprecated code.
 
 # Upgrade to 4.0
 
+## BC BREAK: removed support for the "platform" parameter of the wrapper `Connection`.
+
+The support for the "platform" parameter of the wrapper `Connection` has been removed.
+
 ## BC BREAK: removed support for "unique" and "check" column properties.
 
 The "unique" and "check" column properties are no longer supported.
diff --git a/src/Connection.php b/src/Connection.php
index 55c0aef49b3..091f0f73607 100644
--- a/src/Connection.php
+++ b/src/Connection.php
@@ -20,7 +20,6 @@
 use Doctrine\DBAL\Exception\CommitFailedRollbackOnly;
 use Doctrine\DBAL\Exception\ConnectionLost;
 use Doctrine\DBAL\Exception\DriverException;
-use Doctrine\DBAL\Exception\InvalidPlatformType;
 use Doctrine\DBAL\Exception\NoActiveTransaction;
 use Doctrine\DBAL\Exception\SavepointsNotSupported;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
@@ -134,25 +133,8 @@ public function __construct(
     ) {
         $this->_config       = $config ?? new Configuration();
         $this->_eventManager = $eventManager ?? new EventManager();
-
-        if (isset($params['platform'])) {
-            if (! $params['platform'] instanceof Platforms\AbstractPlatform) {
-                throw InvalidPlatformType::new($params['platform']);
-            }
-
-            Deprecation::trigger(
-                'doctrine/dbal',
-                'https://github.com/doctrine/dbal/pull/5699',
-                'The "platform" connection parameter is deprecated.'
-                    . ' Use a driver middleware that would instantiate the platform instead.',
-            );
-
-            $this->platform = $params['platform'];
-            $this->platform->setEventManager($this->_eventManager);
-        }
-
-        $this->params     = $params;
-        $this->autoCommit = $this->_config->getAutoCommit();
+        $this->params        = $params;
+        $this->autoCommit    = $this->_config->getAutoCommit();
     }
 
     /**
@@ -880,10 +862,7 @@ public function executeCacheQuery(string $sql, array $params, array $types, Quer
             throw NoResultDriverConfigured::new();
         }
 
-        $connectionParams = $this->params;
-        unset($connectionParams['platform']);
-
-        [$cacheKey, $realKey] = $qcp->generateCacheKeys($sql, $params, $types, $connectionParams);
+        [$cacheKey, $realKey] = $qcp->generateCacheKeys($sql, $params, $types, $this->params);
 
         $item = $resultCache->getItem($cacheKey);
 
diff --git a/src/DriverManager.php b/src/DriverManager.php
index 6e9d995d6b7..bcb72b1c695 100644
--- a/src/DriverManager.php
+++ b/src/DriverManager.php
@@ -44,7 +44,6 @@
  *     password?: string,
  *     path?: string,
  *     pdo?: \PDO,
- *     platform?: Platforms\AbstractPlatform,
  *     port?: int,
  *     user?: string,
  *     unix_socket?: string,
@@ -65,7 +64,6 @@
  *     password?: string,
  *     path?: string,
  *     pdo?: \PDO,
- *     platform?: Platforms\AbstractPlatform,
  *     port?: int,
  *     primary?: OverrideParams,
  *     replica?: array<OverrideParams>,
@@ -171,7 +169,6 @@ private function __construct()
      *     password?: string,
      *     path?: string,
      *     pdo?: \PDO,
-     *     platform?: Platforms\AbstractPlatform,
      *     port?: int,
      *     primary?: OverrideParams,
      *     replica?: array<OverrideParams>,
diff --git a/src/Exception/InvalidPlatformType.php b/src/Exception/InvalidPlatformType.php
deleted file mode 100644
index b9313122576..00000000000
--- a/src/Exception/InvalidPlatformType.php
+++ /dev/null
@@ -1,37 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Doctrine\DBAL\Exception;
-
-use Doctrine\DBAL\Exception;
-use Doctrine\DBAL\Platforms\AbstractPlatform;
-
-use function get_debug_type;
-use function is_object;
-use function sprintf;
-
-/** @psalm-immutable */
-final class InvalidPlatformType extends Exception
-{
-    public static function new(mixed $invalidPlatform): self
-    {
-        if (is_object($invalidPlatform)) {
-            return new self(
-                sprintf(
-                    'Option "platform" must be a subtype of %s, instance of %s given.',
-                    AbstractPlatform::class,
-                    get_debug_type($invalidPlatform),
-                ),
-            );
-        }
-
-        return new self(
-            sprintf(
-                'Option "platform" must be an object and subtype of %s. Got %s.',
-                AbstractPlatform::class,
-                get_debug_type($invalidPlatform),
-            ),
-        );
-    }
-}
diff --git a/tests/ConnectionTest.php b/tests/ConnectionTest.php
index 6c7d2057764..8800637082d 100644
--- a/tests/ConnectionTest.php
+++ b/tests/ConnectionTest.php
@@ -25,7 +25,6 @@
 use PHPUnit\Framework\TestCase;
 use Psr\Cache\CacheItemInterface;
 use Psr\Cache\CacheItemPoolInterface;
-use stdClass;
 
 /**
  * @requires extension pdo_mysql
@@ -712,103 +711,6 @@ public function testConnectionParamsArePassedToTheQueryCacheProfileInExecuteCach
 
         (new Connection($this->params, $driver))->executeCacheQuery($query, $params, $types, $queryCacheProfileMock);
     }
-
-    public function testShouldNotPassPlatformInParamsToTheQueryCacheProfileInExecuteCacheQuery(): void
-    {
-        $cacheItemMock = $this->createMock(CacheItemInterface::class);
-        $cacheItemMock->method('isHit')->willReturn(true);
-        $cacheItemMock->method('get')->willReturn(['realKey' => []]);
-
-        $resultCacheMock = $this->createMock(CacheItemPoolInterface::class);
-
-        $resultCacheMock
-            ->expects(self::atLeastOnce())
-            ->method('getItem')
-            ->with('cacheKey')
-            ->willReturn($cacheItemMock);
-
-        $queryCacheProfileMock = $this->createMock(QueryCacheProfile::class);
-
-        $queryCacheProfileMock
-            ->method('getResultCache')
-            ->willReturn($resultCacheMock);
-
-        $query = 'SELECT 1';
-
-        $connectionParams = $this->params;
-
-        $queryCacheProfileMock
-            ->expects(self::once())
-            ->method('generateCacheKeys')
-            ->with($query, [], [], $connectionParams)
-            ->willReturn(['cacheKey', 'realKey']);
-
-        $connectionParams['platform'] = $this->createMock(AbstractPlatform::class);
-
-        $driver = $this->createMock(Driver::class);
-
-        (new Connection($connectionParams, $driver))->executeCacheQuery($query, [], [], $queryCacheProfileMock);
-    }
-
-    /** @psalm-suppress InvalidArgument */
-    public function testThrowsExceptionWhenInValidPlatformSpecified(): void
-    {
-        $connectionParams             = $this->params;
-        $connectionParams['platform'] = new stdClass();
-
-        $driver = $this->createMock(Driver::class);
-
-        $this->expectException(Exception::class);
-
-        new Connection($connectionParams, $driver);
-    }
-
-    public function testExecuteCacheQueryStripsPlatformFromConnectionParamsBeforeGeneratingCacheKeys(): void
-    {
-        $driver = $this->createMock(Driver::class);
-
-        $platform = $this->createMock(AbstractPlatform::class);
-
-        $queryCacheProfile = $this->createMock(QueryCacheProfile::class);
-
-        $resultCache = $this->createMock(CacheItemPoolInterface::class);
-
-        $queryCacheProfile
-            ->method('getResultCache')
-            ->willReturn($resultCache);
-
-        $cacheItemMock = $this->createMock(CacheItemInterface::class);
-        $cacheItemMock->method('isHit')->willReturn(true);
-        $cacheItemMock->method('get')->willReturn(['realKey' => []]);
-
-        $resultCache
-            ->expects(self::atLeastOnce())
-            ->method('getItem')
-            ->with('cacheKey')
-            ->willReturn($cacheItemMock);
-
-        $query = 'SELECT 1';
-
-        $params = [
-            'dbname' => 'foo',
-            'platform' => $platform,
-        ];
-
-        $paramsWithoutPlatform = $params;
-        unset($paramsWithoutPlatform['platform']);
-
-        $queryCacheProfile
-            ->expects(self::once())
-            ->method('generateCacheKeys')
-            ->with($query, [], [], $paramsWithoutPlatform)
-            ->willReturn(['cacheKey', 'realKey']);
-
-        $connection = new Connection($params, $driver);
-
-        self::assertSame($params, $connection->getParams());
-
-        $connection->executeCacheQuery($query, [], [], $queryCacheProfile);
-    }
 }
 
 interface ConnectDispatchEventListener
diff --git a/tests/DriverManagerTest.php b/tests/DriverManagerTest.php
index 6fc0d616569..4fe99ef6bba 100644
--- a/tests/DriverManagerTest.php
+++ b/tests/DriverManagerTest.php
@@ -11,7 +11,6 @@
 use Doctrine\DBAL\Driver\SQLSrv\Driver as SQLSrvDriver;
 use Doctrine\DBAL\DriverManager;
 use Doctrine\DBAL\Exception;
-use Doctrine\DBAL\Platforms\AbstractPlatform;
 use PHPUnit\Framework\TestCase;
 use stdClass;
 
@@ -37,19 +36,6 @@ public function testInvalidDriver(): void
         DriverManager::getConnection(['driver' => 'invalid_driver']);
     }
 
-    /** @requires extension pdo_sqlite */
-    public function testCustomPlatform(): void
-    {
-        $platform = $this->createMock(AbstractPlatform::class);
-        $options  = [
-            'url' => 'sqlite::memory:',
-            'platform' => $platform,
-        ];
-
-        $conn = DriverManager::getConnection($options);
-        self::assertSame($platform, $conn->getDatabasePlatform());
-    }
-
     /** @requires extension pdo_sqlite */
     public function testCustomWrapper(): void
     {
diff --git a/tests/Exception/InvalidPlatformTypeTest.php b/tests/Exception/InvalidPlatformTypeTest.php
deleted file mode 100644
index 0c3b1a6c7e0..00000000000
--- a/tests/Exception/InvalidPlatformTypeTest.php
+++ /dev/null
@@ -1,35 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Doctrine\DBAL\Tests\Exception;
-
-use Doctrine\DBAL\Exception\InvalidPlatformType;
-use Doctrine\DBAL\Platforms\AbstractPlatform;
-use PHPUnit\Framework\TestCase;
-use stdClass;
-
-class InvalidPlatformTypeTest extends TestCase
-{
-    /** @group #2821 */
-    public function testInvalidPlatformTypeObject(): void
-    {
-        $exception = InvalidPlatformType::new(new stdClass());
-
-        self::assertSame(
-            'Option "platform" must be a subtype of ' . AbstractPlatform::class . ', instance of stdClass given.',
-            $exception->getMessage(),
-        );
-    }
-
-    /** @group #2821 */
-    public function testInvalidPlatformTypeScalar(): void
-    {
-        $exception = InvalidPlatformType::new('some string');
-
-        self::assertSame(
-            'Option "platform" must be an object and subtype of ' . AbstractPlatform::class . '. Got string.',
-            $exception->getMessage(),
-        );
-    }
-}
diff --git a/tests/ExceptionTest.php b/tests/ExceptionTest.php
index ffea14412b0..35b257aaa58 100644
--- a/tests/ExceptionTest.php
+++ b/tests/ExceptionTest.php
@@ -5,10 +5,7 @@
 namespace Doctrine\DBAL\Tests;
 
 use Doctrine\DBAL\Exception\DriverRequired;
-use Doctrine\DBAL\Exception\InvalidPlatformType;
-use Doctrine\DBAL\Platforms\AbstractPlatform;
 use PHPUnit\Framework\TestCase;
-use stdClass;
 
 use function sprintf;
 
@@ -28,25 +25,4 @@ public function testDriverRequiredWithUrl(): void
             $exception->getMessage(),
         );
     }
-
-    public function testInvalidPlatformTypeObject(): void
-    {
-        $exception = InvalidPlatformType::new(new stdClass());
-
-        self::assertSame(
-            'Option "platform" must be a subtype of Doctrine\DBAL\Platforms\AbstractPlatform, '
-                . 'instance of stdClass given.',
-            $exception->getMessage(),
-        );
-    }
-
-    public function testInvalidPlatformTypeScalar(): void
-    {
-        $exception = InvalidPlatformType::new('some string');
-
-        self::assertSame(
-            'Option "platform" must be an object and subtype of ' . AbstractPlatform::class . '. Got string.',
-            $exception->getMessage(),
-        );
-    }
 }