Source Reference:

• Component: bbPress :: bbp-topic

  File: /bbp-includes/bbp-topic-template.php :: Trac Source Line: 1618

  	function bbp_get_topic_last_reply_url( $topic_id = 0 ) {
  		$topic_id = bbp_get_topic_id( $topic_id );
  		$reply_id = bbp_get_topic_last_reply_id( $topic_id );
  
  		if ( !empty( $reply_id ) && ( $reply_id != $topic_id ) )
  			$reply_url = bbp_get_reply_url( $reply_id );
  		else
  			$reply_url = bbp_get_topic_permalink( $topic_id );
  
  		return apply_filters( 'bbp_get_topic_last_reply_url', $reply_url );
  	}
  
  /**
   * Output link to the most recent activity inside a topic, complete with link
   * attributes and content.
   *
   * @since bbPress (r2625)
   *
   * @param int $topic_id Optional. Topic id
   * @uses bbp_get_topic_freshness_link() To get the topic freshness link