Songwriter Tony Mortimer rejoined the 1990s boyband for a comeback show in 2006 but the group soon split again after a falling out.
Mortimer had been booked to play the Wild & Live show at London's Royal Albert Hall this Saturday as a solo artist but asked along former bandmates Brian Harvey, Terry Coldwell and John Hendy, The Sun reports.
Harvey said: "The last reunion was a bit of a rushed job, we had to do a gig and documentary. It got a bit out of hand because time was against us.
"This time around we'll be performing two tracks, 'Deep' and 'Stay Another Day', and are just going to enjoy it. We're too old to fall out."
Mortimer added: "There's no pressure, we're taking things easy. It's all about getting on at the moment.
"There's no plans for an album or tour. What happened is in the past now - it's all water under the bridge."
Other acts who will feature at the Born Free Foundation gig include Peter Andre and Mutya Buena, who will perform a duet of Andre's new single 'Unconditional'.
> Whatever happened to... East 17?