Get the tissues ready!

On Comedy Central's Night of Too Many Stars (previously recorded on Oct. 13), Katy Perry sang a moving duet with a young autistic girl, Jodi DiPiazza. The talented young musician began performing the pop star's hit song, "Firework," while playing the piano. 

Shortly into the song, Perry, 27, joined DiPiazza on stage. The duet moved host Jon Stewart to tears and earned a standing ovation from the audience.

"It's the most beautiful thing I've ever been associated with," said the comedian Robert Smigel, who produces Night of Too Many Stars, to the Associated Press. "I've made a career of all this nonsense -- and I'm very proud of it -- but it all pales in comparison to what happened Saturday."

After the show, Perry tweeted, "I will never forget last night. It was the most important moment thus far of what I do." 

Watch the touching video above. Night of Too Many Stars airs Sunday, Oct. 21 at 8:00 EST on Comedy Central.