diff --git a/includes/core/class-pr-core-related-posts-section.php b/includes/core/class-pr-core-related-posts-section.php
new file mode 100644
index 0000000..6d65ada
--- /dev/null
+++ b/includes/core/class-pr-core-related-posts-section.php
@@ -0,0 +1,126 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Renders the related articles section on peptide single pages.
+ *
+ * What: Hooks into pr_core_after_peptide_content and renders a card grid
+ *       of related posts fetched via PR_Core_Related_Posts_Provider.
+ * Who calls it: PR_Core::init() instantiates and registers hooks.
+ * Dependencies: PR_Core_Related_Posts_Provider interface, template-parts/related-posts/card.php.
+ *
+ * Settings read:
+ * - pr_core_related_posts_enabled (bool, default true)
+ * - pr_core_related_posts_limit (int, default 3, range 1-6)
+ */
+class PR_Core_Related_Posts_Section {
+
+	/** @var PR_Core_Related_Posts_Provider */
+	private $provider;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param PR_Core_Related_Posts_Provider $provider Provider instance.
+	 */
+	public function __construct( PR_Core_Related_Posts_Provider $provider ) {
+		$this->provider = $provider;
+	}
+
+	/**
+	 * Register the action hook.
+	 *
+	 * @return void
+	 */
+	public function register_hooks(): void {
+		add_action( 'pr_core_after_peptide_content', [ $this, 'render' ] );
+		add_action( 'save_post_post', [ $this, 'invalidate_caches' ] );
+	}
+
+	/**
+	 * Render the related posts section.
+	 *
+	 * Called via do_action( 'pr_core_after_peptide_content', $peptide_id ) in templates.
+	 * If feature disabled or no posts found, renders nothing.
+	 *
+	 * @param int $peptide_id The peptide post ID.
+	 * @return void
+	 */
+	public function render( int $peptide_id ): void {
+		$enabled = (bool) get_option( 'pr_core_related_posts_enabled', true );
+		if ( ! $enabled ) {
+			return;
+		}
+
+		$limit = (int) get_option( 'pr_core_related_posts_limit', 3 );
+		$limit = min( 6, max( 1, $limit ) );
+
+		$posts = $this->provider->get_posts( $peptide_id, $limit + 5 );
+		if ( empty( $posts ) ) {
+			return;
+		}
+
+		$peptide = get_post( $peptide_id );
+		?>
+		<section class="pr-related-posts" aria-label="<?php esc_attr_e( 'Related Articles', 'peptide-repo-core' ); ?>">
+			<h2><?php esc_html_e( 'Related Articles', 'peptide-repo-core' ); ?></h2>
+			<div class="pr-related-posts__grid">
+				<?php
+				$count = 0;
+				foreach ( $posts as $post ) {
+					if ( $count >= $limit ) {
+						break;
+					}
+					setup_postdata( $post );
+					get_template_part( 'template-parts/related-posts/card', null, [ 'post' => $post ] );
+					++$count;
+				}
+				wp_reset_postdata();
+				?>
+			</div>
+			<?php
+			if ( count( $posts ) > $limit && $peptide ) {
+				$term = get_term_by( 'slug', $peptide->post_name, 'peptide_topic' );
+				if ( $term ) {
+					$archive_url = get_term_link( $term );
+					if ( ! is_wp_error( $archive_url ) ) {
+						?>
+						<p class="pr-related-posts__view-all">
+							<a href="<?php echo esc_url( $archive_url ); ?>">
+								<?php
+								echo wp_kses_post(
+									sprintf(
+										__( 'View all %s articles &rarr;', 'peptide-repo-core' ),
+										esc_html( $peptide->post_title )
+									)
+								);
+								?>
+							</a>
+						</p>
+						<?php
+					}
+				}
+			}
+			?>
+		</section>
+		<?php
+	}
+
+	/**
+	 * Invalidate related posts transient caches when a post is saved.
+	 *
+	 * Hooks into save_post_post to clear any cached related-post queries
+	 * since the post corpus has changed.
+	 *
+	 * @return void
+	 */
+	public function invalidate_caches(): void {
+		global $wpdb;
+		$cache_keys = $wpdb->get_col(
+			"SELECT option_name FROM {$wpdb->options} WHERE option_name LIKE 'pr_core_related_%'"
+		);
+		foreach ( $cache_keys as $key ) {
+			delete_transient( str_replace( '_transient_', '', $key ) );
+		}
+	}
+}