Once upon a time an ogre married a princess and they had three children. One of their kids was named Fergus. We never see him grow up. BUT, in the movie Brave, there's a king named Fergus. Now, keep in mind that Princess Fiona was cursed, and alternated from her human form to her ogre form. Maybe the ogre, Prince Fergus, took a potion to change him into a human. Even the timeline seems right at first glance; what with swords, and horse carriages...Maybe Shrek is the grandfather to Princess Merida.

No, hear me out. Think about this for a second.

Prince Fergus has red hair. King Fergus has red hair. Prince Fergus has a Scottish accent. King Fergus has a Scottish accent. But wait! What about their eyes? True, One of them has blue eyes and one of them has brown. BUT I used to have blue eyes and red hair, and now I have green eyes and brown hair. Things change. I mean, hell! What if Merida's red hair and blue eyes come not just from King Fergus, but Princess Fiona?

And you know who else has brown hair and green eyes? Aunt Cass. Maybe Rapunzel was her ancestress.

But then there's Honey Melon, with her long blond hair and familiar green eyes...Maybe, like Rapunzel, she possesses magic hair.

Maybe they're both related to Rapunzel. Or perhaps the duplicate theories strewn over YouTube are onto something, and the old witch from Brave was a time-traveller. In this sense, it would even be plausible that Rapunzel discovered a way to whisk herself off to the future.