JUST ADDED: 5 Seconds of Summer will be rocking the stage at this year's iHeartRadio Music Festival Village in Las Vegas! The band sat down with Ryan Seacrest to break the news. Click here to buy your tickets now, before they sell out!
"Ignition (Remix)" is an R. Kelly classic .. but we bet you've never heard it sung by a barber shop quartet!
As Jimmy Fallon continues to kick off the new "Tonight Show," he performed R. Kelly's smash hit ... along with his barber shop quartet, The Ragtime Gals. And in full barber shop quartet fashion!
Check it out below!