The Take That star will step in for the 'Dancing on the Ceiling' hitmaker - who was forced to cancel his scheduled headlining slot at Sunday's (11.09.11) London show due to illness - and the 'x factor' judge revealed he jumped at the chance when he was approached by DJ Chris Evans.
He said: "It's a pleasure to step in last minute and cover for Mr. Richie. Chris called me and said Lionel had had to pull out because he was ill and they had a hole in the show, so I was more than happy to help out."
Chris added: "What an incredible line-up -thanks to super-sub Gary Barlow, who is now the icing on what was already a special cake! It promises to be a terrific day of entertainment at Radio 2 Live in Hyde Park!"
Tickets for Radio 2 Live in Hyde Park are still available.