public function add_orphaned_columns( $event_id ) {
		// Go through the event attendees and get the fields.
		foreach ( Tribe__Tickets__Tickets::get_event_attendees( $event_id ) as $attendee ) {
			// Get the meta fields of that attendee.
			$meta_fields = get_post_meta( $attendee['attendee_id'], Tribe__Tickets_Plus__Meta::META_KEY, true );

			// If we have some meta fields.
			if ( ! is_array( $meta_fields ) ) {
				return;
			}

			// Go through the meta fields.
			foreach ( $meta_fields as $key => $value ) {
				$this->add_orphaned_column( $key );
			}
		}
	}