Demi Lovato and Alanis Morissette teamed up to deliver an epic duet of the latter's '90s hit, "You Oughta Know," at the American Music Awards on Sunday. 

Lovato returned to the stage -- with slightly messier hair -- following her solo performance of "Confident" earlier in the evening, trading verses with Morissette on the breakup anthem.

PICS: 2015 American Music Awards Red Carpet Style

It's been 20 years since Morissette's breakthrough album, Jagged Little Pill, was released, and the singer has been celebrating the milestone all year long.

"I just remember not wanting to stop until I wrote a record that really represented where I was at and all my humanity," Morissette told ETonline in June. "I really did think I was the only human being on the planet going through whatever it was that I was going through at the time. So when people connected with it in the way they did, I felt less alone."

WATCH: How 'Jagged Little Pill' Changed Everything & What Alanis Morissette Thinks About It Now

Earlier this month, Morissette teamed with Meghan Trainor (who is also performing on Sunday's AMAs) to perform a clucking rendition of "Ironic" on The Tonight Show.

See the bizarre performance in the video below.