Band members Gareth Gates, Dane Bowers, Adam Rickitt, Kavana and Blazin' Squad's Kenzie watched the episode nervously during a break in reherasals.
But they needn't have worried, as the newly-formed group is obviously a hit already!
Last night, Kenzie tweeted: "What a show! The feedback has been amazing for @WeAre5thStory. Hope you all enjoyed it and thank you for the support #BigReunion2014 x."
Rather than the episode being split between two Big Reunion bands like in previous weeks, last night's show was purely dedicated to 5th Story.
It looked at the highs and lows of each star's career and there were definitely some awkward moments - especially for Gareth!
Wow that was hard to watch— Gareth Gates (@Gareth_Gates) February 20, 2014
Pop Idol runner-up Gareth spoke about his relationship with Katie Price and was even shown discussing it with his mum.
During the show, he tweeted: "Wow that was hard to watch."
Meanwhile, Dane talked about his rise to fame with Another Level and admitted that his dad had to pay his mortgage when the band split.
He also touched upon the time he was arrested on suspicion of conspiracy to commit rape in 2012. All charges were dropped but Dane said: "When people Google me now it says 'aggravated assault', 'conspiracy to commit rape', which people read as 'rape'.
"Every single one of those was dropped, the press wouldn't write the story that I'm innocent."
After watching the show, Dane also tweeted: "Thanks everyone for the nice tweets about @WeAre5thStory . Been an emotional one already but looking forward to Hammersmith tomorrow now!!"
Tonight, 5th Story will join their fellow Big Reunion bands - 3T, Girl Thing, Eternal, A1 and Damage - for their first concert at the Hammersmith Apollo in London.
The Big Reunion 2014: Now and then
Copyright: Rex Features