diff --git a/src/wp-includes/class-wp-query.php b/src/wp-includes/class-wp-query.php
index f088bda6da..51cd8b1084 100644
--- a/src/wp-includes/class-wp-query.php
+++ b/src/wp-includes/class-wp-query.php
@@ -480,6 +480,7 @@ class WP_Query {
 	 * The cache key is generated by the method ::generate_cache_key() after the
 	 * query has been normalized.
 	 *
+	 * @since 6.8.0
 	 * @var string
 	 */
 	private $query_cache_key = '';