Kristene

Kristene (also known as Eugoff or Flynnoff) is the name for the pairing between Kristoff Bjorgman and Eugene Fitzherbert from Frozen (2013) and Tangled (2010). It is not a popular pairing in the fandom, but it does have a good number of fans.

Relationship Overview
Many fans believe that Kristoff and Eugene could meet when Eugene attends Elsa's coronation with Rapunzel. Both being fun-loving boyfriends of young, naive princesses, they could sympathize with each other's challenges in life and become good friends, with Eugene offering romantic advice to Kristoff. Some suppose that the two could even become a bit more than good friends.

This could also happen in a universe where Flynn and Kristoff never meet their respective princesses, probably running into each other when Flynn is up in Arendelle to scout out a burglary target and Kristoff is in town to sell ice at the market. In this scenario, it's far more likely for the two to become romantic faster, whether Kristoff stops the burglary or not.

Popular AU

 * Modern AU
 * War AU

Fanfiction
Note: Only list examples from within the RotBTD fandom