The 'Angels' singer has admitted he found it hard to forgive the Take That songwriter when he left the band in 1995 and even after seeing his former friend struggle to establish a solo career following the demise of the group, he couldn't let go of his bitter feelings.
Robbie – who has now ended his feud with Gary and rejoined the group for a new LP and tour – said: "My problem has always been with Gary. It was always with Gary. I wanted to crush him. I wanted to crush the memory of the band – and I didn't let go.
"You know, even when he was down, I didn't let go. And for that I sincerely apologise."
Meanwhile, Gary has admitted he begged his bank to change the name on his credit cards after his career flopped while Robbie's took off because he couldn't take anymore ridicule.
He said: "It was hard watching Rob get further and further into the distance and I just seemed like I'd gone 10 steps back.
"It was a constantly daily mock. It followed me everywhere. You just seem like a total loser.
"In fact, I remember asking the bank whether I could change my name on my card. I couldn't face my own name because even over the phone people would make some wisecrack."
Though Take That – also comprising of Howard Donald, Mark Owen and Jason Orange – are preparing to release their first album as a five-piece in 15 years and will embark on a mammoth European tour next year, their reunion was thrown into doubt after Robbie again quit the group last November following a brief appearance together, saying he wasn't ready.
He explains in new documentary 'Take That: Look Back, Don't Stare': "I wasn't very well, physically. I just didn't feel as if I had the energy to do it.
"It was a scary prospect to be out there among something so huge feeling depleted of life force."
Though he was eventually talked round by Mark, Jason was furious with the 'No Regrets' singer's actions.
He said: "It was like the rug was pulled from under my feet. I was gutted. I actually said to Rob, 'Your whims have a direct effect on us.' "
'Take That: Look Back, Don't Stare' airs in the UK on ITV1 on Saturday (13.11.10) night.