The Take That frontman has revealed he and the former 'Neighbours' star, 50 - who have been friends for many years - would impersonate celebrities, including the 85-year-old acting legend and singer Sir Cliff Richard, when they went on joint holidays with their wives.
All while their respective spouses, Dawn Barlow Angela Donovan, would laugh at how ''immature'' they were.
According to the Daily Star newspaper, the 47-year-old singer - who has son Daniel, 18, and daughters Emily, 16, and Daisy, nine, with Dawn - recalled: ''Our favourite holiday are when we are away with Jason and Ange Donovan.
''All kids all went to school together, they're all the same age and they get on great.
''Together, Jason and I became an act.
''The girls sit and talk about us right in our faces, our harshest critics.
''They're like the two old dudes in The Muppets, up in the royal box, passing comment, mostly on how immature we are.''
When Jason took part in 'Strictly Come Dancing' in 2011 - which saw him come third place with former professional dance partner Kristina Rihanoff - Gary decided to put on a voice that was a mix between Sir David Attenborough and late co-host of the BBC ballroom and Latin show, Sir Bruce Forsyth.
In an excerpt from his book 'A Better Me', he said that Jason - who has Zac, 17, and daughters Jemma, 18, and seven-year-old Molly with his wife - was ''going to start practising early for Strictly'' and was ''dancing around the swimming pool for two hour a day with a mop''.
He recalled: ''We all sat and judged him. Everyone's watching from behind their hands.''
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