Board Thread:News and Announcements/@comment-24580673-20140223024405/@comment-24362388-20140223160034

He could have a sister aswell, but he HAS to have a brother for Dipper and Mabel to have the surname Pines, because if he was related to their grandma, (not by marrage, but blood), they would have a different surname (well, there is a 99% chance)