Sherri and Terri's sister

Sherri and Terri's Sister is the sister of twins Sherri and Terri. She was mentioned by Dr. J. Loren Pyror during his meeting with Bart; during this, he stated that Sherri, Terri, and the unnamed sister were conjoined triplets and the third triplet is out seeking revenge after being separated from her sisters.

Trivia

 * The sister is a callback to Hugo Simpson, a character featured in the non-canon Treehouse of Horror who was Bart's conjoined twin. Like the sister, he was separated from Bart at birth.