Thomas Brodie-Sangster and Olivia Olson worked together previously in 'Love, Actually,' where their characters were also connected romantically.
Madison Pettis and Ariel Winter are the only Fireside Girl voices who play their respective characters as both children and teens.
The story originally ended with Phineas and Isabella hugging as she left for college. Series co-creator Dan Povenmire felt it needed something more, so after initial viewing the episode, he added in an extra scene where he meets up with her and they kiss.