Betty Grof

Betty was a human woman revealed to have once been the fiancée of a man named Simon Petrikov, who would much later become Ice King. She and Petrikov had a very committed relationship until Petrikov obtained an enchanted crown, which gradually began to alter his mind and body. When Petrikov put on the crown for the first time, something he did terrified Betty and caused her to leave. Simon never saw her again, and he records on video his desperate wish to regain his sanity so that she might one day return to him. It is not known if she was killed during the Mushroom War.

Trivia

 * Simon referred to Betty as his princess while he still possessed some of his sanity. This may explain his obsession with Princesses.
 * In one of the pictures, Betty is wearing a lab coat. This might mean that she was in a field of study, such as science or medical.
 * Adam Muto stated that the figure in the picture with Ice King and Betty is "some sort of cryptid."