The global stars of Olympic gymnastics aligned to put on a spectacular show led by Biles and Whitlock.
Biles' entrance was pure Hollywood, beaming a smile to a packed crowd at the O2 stadium.
And while wowing the crowd with her exhibition performances, the four-time Olympic champion clearly enjoyed her new role as judge too.
So used to being on the other side of the table, this event was a new experience for the American as she sat in the judges' dock for the first time, joined by an all-star panel in Max Whitlock, Amy Tickler and Laurent Landi.
It was 'The X Factor' for gymnastics.
"We've never done anything like this before, so it was a chance to do something very different. Because it's a showcase it means you can go out there and have a lot more fun," - Simone Biles
The show was designed to give gymnasts a different platform to express themselves and enjoy themselves.
Each performance was scored out of 10, with no code of points and an emphasis on flair, creative choreography, execution and engagement with the live crowd.
While Biles and Whitlock did not compete, they did perform. Biles opened the afternoon session and ended the evening session with an exhibition and the Briton showed his stuff to bring the afternoon session to a close, then opened the evening event.
Check out Biles' floor routine here:
Whitlock took a time out from his usual training schedule and new responsibilities as a father to star in the show.
He and his wife Leah celebrated the birth of daughter Willow this year, but Max is still training hard with Tokyo 2020 on the horizon.
The Team GB double gold medallist said the 'Gymstars' show was a chance for gymnastics to engage with a wider audience and for the sport to try out new things.
“I think it’s very important that the sport can evolve,” the 26-year-old Whitlock, who became Britain’s first Olympic gold medallist in artistic gymnastics by winning floor and pommel in Rio, told Reuters.
Before the beginning of the show he sat down for an interview with Simone Biles and was full of praise for his fellow judge.
"She is an incredible gymnast, an inspiration to so many youngsters in this country and in every country." - Max Whitlock
"I have been looking forward to this for so long," Whitlock continued, speaking about the gala.
"Events like this are what gymnastics has needed for a very long time. As a gymnast, for our sport we need to push it as far as we possibly can and our mission has always been to inspire the next generation."
"We are bringing something that hasn't been seen before. The gymnasts have the freedom to perform anything they want to wow the crowd - Max Whitlock
"That might bring something you've never seen before; it is very exciting. Our sport has come on leaps and bounds and this is a way to continue that."
A stellar cast of Olympic and world champions also lined up for this new event, including Germany's Fabian Hambüchen, a Rio 2016 horizontal bars gold medallist, double Olympic silver medallist Marcel Nguyen, and three-time world champion gymnast Oksana Chusovitine.
Artistic gymnast Danusia Francis won the crowd and judges over with a performance that drew tens all round.
Her dismount and nod to Usain Bolt had the crowd begging for more.
British gymnast Courtney Tulloch topped the podium twice at the Commonwealth Games in the rings and team events, but could the Lewisham native get the crowd on his side in London?
Of course he could!
Marcel Nguyen won two Olympic silver medals at London 2012 in Parallel bars and All-Around events, but his flossing on the parallel bars was what really got the crowd going in London.
The judges liked it, a lot, giving him the first 80-point routine of the day.
Floss on Marcel!
It wasn't all seasoned-pros strutting their stuff though, there was room for the younger generation to show what they can do too.
Halle Hilton is just 14, but is already making a name for herself after taking bronze in the Junior team event at the European Championships in Glasgow last year.
She put on a balance beam exhibition and the crowd loved it.