Last night's X Factor live show had a bit of unexpected drama when boy band Stereo Kicks gained an extra member during their performance.

While many viewers at home might not have noticed that the eight-strong group had gone up to nine, the boys themselves and the watching judges were baffled by the appearance of comedian Lee Nelson on stage.

Dressed in a natty red jacket and jeans, with perfectly styled hair, the TV funnyman (real name Simon Brodkin) wandered around on stage miming and attempting to interact with the lads as they sang Michael Jackson's You Are Not Alone (irony alert!).

However he was quickly bundled off stage by security staff - with many viewers not realising he'd even been there until the judges mentioned it afterwards.

Mel B referred to him as an "idiot imposter" and Cheryl Fernandez-Versini praised them for staying "professional".

Simon Cowell said that "these things happen on live TV" and joked that mentor Louis Walsh was trying to sneak them up to nine members.

Nelson is known for his pranks, including dressing up as a member of the England football team and attempting to board their coach.

Stereo Kicks were top lads. Still think they'd be better off with 9. I'd vote for them but Cowell's got my phone pic.twitter.com/tmj4tO6XZH

— Lee Nelson (@RealLeeNelson) November 8, 2014