public function onDeleteRelation($event)
    {
        $sender = $event->sender;
        /* @var $sender static */
        if ($sender->relationType == static::$relationMutual) {
            $sender->off(static::EVENT_AFTER_DELETE, [$sender, 'onDeleteRelation']);
            static::removeAllRelations($sender->recipient, $sender->initiator);
            $sender->on(static::EVENT_AFTER_DELETE, [$sender, 'onDeleteRelation']);
        }
    }