The American girl group finished in third place on the 2012 series of US X Factor and have since gone on to sign a record deal with Simon Cowell's label Syco.
Unsurprisingly, the music mogul has now invited the pop band over to the UK sing on our version of the show on 7 December.
Announcing the news on Twitter, Fifth Harmony - made up of Ally Brooke Hernandez, Normani Hamilton, Dinah Jane Hansen, Camila Cabello, and Lauren Jauregui - could barely contain their excitement!
"We're so excited to announce that we're going to be on X Factor UK! Make sure you tune in on December 7th Harmonizers!" they gushed.
Taking over the official US X Factor account, the girls added: "Are y'all as excited as we are??!?! This is one of the biggest performances we've done so far!!! OMG!!! We can't wait!!!"
Simon mentored Fifth Harmony throughout their time on the TV show and, like One Direction in the UK, were originally individual soloists who were put into a band at the end of Boot Camp.
They started out with the name LYLAS - an acronym for Love You Like A Sister - but later switched to Fifth Harmony as there is already a band in the music industry called The Lylas (which features four of Bruno Mars' sisters!).
Watch Fifth Harmony's final US X Factor performance here: