Did anyone know this before?

It is just a fan fiction, although it could be considered as partially true.

In my fandom, the Queens aren't the ones who are related; but the Queen of Corona and the King of Arendelle are. They have much plus in common. toi may find an article ou post in a La Reine des Neiges fandom site ou in Tumblr

In some other stories, they claim that Ariel's sunken ship may also be the sunken ship of the King and Queen of Arendelle. It could be true since Arendelle is located in Norway, and The Little Mermaid could originate from Denmark.

If toi take the Coronation Cameo Theory of the fandom, the ship may have passed par Denmark on it's way to the Kingdom of Corona in Germany. It may have sunk there.

It's funny on how everything is connected in most Disney Princess movies.

Here's a link to better explain the answer:
link

Uh.. I do not think so... I think Anna, Rapunzel and Elsa are just friends

no i didn't

that's true

Yeah, I've heard of things like this before. It could be true.

It's an Easter egg, planted from the animators to montrer the connection between Raiponce and Frozen, so yes, it is true.