With the portal open, he took the moment to attempt to apologize to Betty, but instead she leapt into the future to be with him, thus explaining why Simon never saw her again in the past.
Back to normal, he enlisted Marceline, Finn, and Jake to help him create a portal to the past before he drove Betty away, using Hambo as a catalyst. In 'Betty,' Simon regained his sanity after having his ice powers stolen by Bella Noche. As revealed in ' Betty,' when Simon was wearing the crown for the first time, he chased Betty through a town while shooting ice bolts and asking ' Where is my princess?' As he had said 'Betty, my princess' in ' Holly Jolly Secrets Part II,' this likely meant he was looking for her.
