"Doofus Khan! Regent Monogram will have your head!"
Princess Isabella is the princess and ruler of the Tri-Province Area under the guidance of Regent Monogram.
The Princess was kidnapped by Doofus Khan in order to prevent Regent Monogram from countering the Khan's attacks. She was later rescued by Phineas and Ferb and fought against Doof's dragon with them. The Great Wall of China was her idea.
The Princess looks just like her modern day descendant. She wears a purple regal dress with a wide, dark purple belt around her chest. Around her neck is a dark purple xiapei and a black pearl. She wears a pink and purple phoenix crown decorated with a pink bow. The crown has purple wings with three black pearls dangling from each. She has a purple bow on her head and sandals on her feet.
- The xiapei is a decorated, long piece of cloth put around the neck. It is worn by noblewomen and by brides at weddings.