X Factor 2012: The new One Direction? Union J cancel gig over safety fears
The four piece - George Shelley, Jaymi Hensley, JJ Hamblett and Josh Cuthbert - were due to sign autographs and take pictures with fans at Brent Cross Shopping Centre on Thursday night.
But the boys had to pull out amid fears they'd be "mobbed" by the huge number of people they'd attracted.
The band tweeted to their 353,000 followers: "We are SO sorry, just about to leave BUT the security have told us we r not allowed 2 come as its a security risk. We feel awful. So sorry.X.
"To all u amazing people who turned up we are so overwhelmed for your support..it means the world. Tweet us a pic of u now and we will follow."
The boys then uploaded a snap of them holding up apology notes and wrote: "Here is a picture to show how sorry we are.....guys we feel awful for letting you down! It wasn't our fault!"
And upon returning to their hotel, they found a group of excited girls waiting for them to arrive.
Understandably, they seemed pretty chuffed.
It seems these lads could prove a real threat to One Direction, who competed on the show in 2010 and are arguably the biggest band in the world right now.
Nonetheless, 1D singer Harry Styles, 18, recently showed his support for Union J and fellow all-guy-group District 3.
Harry told Heat: "The boybands are really good. I think its good that there are two boybands because a lot of the time I don't really think they want to put two of them through.
"I think they are both really great and talented and they showed that on The X Factor."