Cheryl Fernandez Versini was slammed by The X Factor viewers after she joined her act Reggie N Bollie on stage. Singing Watch Me (Whip/Nae Nae) by Silentó selected for them by the public for Jukebox week, the duo performed with their characteristic high energy for the jaunty song.

It all looked like so much fun that mentor Cheryl couldn't help get up and join them in an impromptu dance-off. But her spontaneous display didn't go down well on Twitter with viewers accusing the Crazy, Stupid Love singer of stealing her act's thunder.

"It's not about her it's about the acts! It's just embarrassing," said one angry fan. "God Cheryl is so annoying! She thinks she is part of the band!" wrote another. "It's meant to be about the CONTESTANTS not the JUDGES. So stupid".

Former X Factor finalist Fleur East saw it all as just a bit of fun. "YES!!! @ReggieNBollie you NEVER let me down!! I love that @CherylOfficial did the azonto with them! I LOVED it!" tweeted the Sax singer.

But Simon Cowell didn't hesitate to accuse Cheryl of showing favoritism for the boys over her other act 4th Impact. "I didn't see you getting on stage with 4th Impact," he said. He was however, supportive of Reggie N Bollie praising their performance. ""You are getting this so right. On the money," he said. While they were once dismissed as a novelty act, the pair have won over the British public and have been described as "national treasures." "You're actually credible recording artists," added Rita Ora.

Someone who didn't get it right on the night was Che Chesterman. Singing what is easily the song of the moment, namely Adele's Hello, the aspiring singer forgot the lyrics. While he struggled through the song, his disappointment was evident, as was the judges. Reacting to the error, Simon said it as it was. "You lost your way with that - so it clearly wasn't a very good performance. I don't know what happened there, but it was very disappointing." "We all make mistakes," added Cheryl. "It happens to the best of us. We've seen Beyonce fall down a flight of stairs and Madonna with her cape, but the crucial thing is that you got back up again".

Rita too acknowledged his efforts saying: "You didn't stop - you get going. Props to you for that - it's the respect you deserve." He did however redeem himself with his second song choice with a soulful version of Otis Readings' Try A Little Tenderness. Even Simon was impressed. "The mark of a man is that he gets back up when he's down/ You did that. Amazing".

It was second chance saloon for most of the acts, who appeared to perform better with their next songs. 4th Impact's version of The Jackson 5 song I'll Be There, had Simon praising their spiraling vocals, but he was still uninspired by their look. Referring to the singers as "A" and "B" he reminded them yet again of the importance of creating individual identities for themselves.

And with their second track they made it clear exactly who they are, appearing as real life dolls in giant boxes emblazoned with their names. In a mash up of Gwen Stefani's Rich Girl and Iggy Azalea's Fancy, the girls danced out of boxes in a show-stopping performance that made them unforgettable. Even Simon was able to remember their names after that.

Louisa Johnson was hailed by the judges as the stand out star of the show and possibly the series, as she opened and closed the show with flawless performance of Labrinth's Jealous. "You're potentially one of the best we've ever had," said Simon.

With just five acts left in the competition, there's definitely a frontrunner, but either way, in the end even without any acts of his own, the biggest winner will be Simon Cowell.