The 18-year-old performed the song at the London night club after squeezing herself into a very Jessie J-inspired cartoon print cat suit for the event.
Writing on Twitter before the sell out show, Cher said: "I can't wait for tonight @JeremyJoseph ! Let's put on a show!!!! See you soon! Xxx"
Want U Back, which features a rap from X Factor USA contestant Astro, is out to download now.
Watch Cher Lloyd at G-A-Y below...