What is Elsa's last name?

She doesn't have one BUT I would name it draaama クイーン for obvious reasons!

Historically speaking, both Anna and Elsa would have taken their father's name as their last name. So, their last name would be Agnarrsdotter.

Side note: If Elsa または Anna were male, instead of Agnarrsdotter, their last name would be Agnarrsson lol