That's So Lannister...

1.

This is Tommen (left) and Myrcella (right) Baratheon, from Game of Thrones. In the show, they are siblings born of incest between brother and sister - Jaime Lannister and Cersei Baratheon.

2.

It has been confirmed that the actors playing the royal siblings, Dean-Charles Chapman & Nell Tiger Free, are dating.

3.

Here's a classic photo of Bran Stark finding out about their incestuous relationship.