Snorkmaiden's Lost Memory Tanoshî Mûmin ikka : Season 1 Episode 15

During a spell of rainy weather Snorkmainden has crammed herself with stories about princesses and chivalrous knights. On the first sunny day she and Moomin climb a mountain, where Snorkmaiden sees what she believes is, an Edelweiss. Needless to say it isn't (no such things in Moominvalley), but they have to climb down to get it. Snorkmaiden slips, rolls down the mountainside and winds up in a faint. When she comes to she has forgotten all, and thinks she is of royal blood...