The 'Candy' singer insists he was happy that his former bandmates - Gary Barlow, Mark Owen, Jason Orange and Howard Donald - decided to perform together again in 2006 but admits he didn't want them to do as well as they went on to.
Robbie - who quit the band in 1995, months before they split, and rejoined in 2010 - admitted: ''When the boys first got together, I was pretty much, 'Oh, right, OK ' ''Then it was, 'They've sold 275,000 tickets... they've done what?!'
''I was gobsmacked. Gobsmacked in all manner of everything. Sort of, 'Wow, we meant that much to people, that's great. They mean that much to people? S**t!'
''I think it was confusion more than anything. [I was] pleased for the boys - you know not too pleased that I wanted them to take over the joint.
''It was like, you know, they can have a certain level. Just don't smash the living daylights out of it, like they did.''
Despite his own hugely successful pop career, 38-year-old Robbie - who recently became a father for the first time when wife Ayda Field gave birth to their daughter Teddy - doesn't think he will leave much of a musical legacy, though he thinks he should be viewed as a ''national treasure''.
Speaking to James Corden for forthcoming documentary 'When Robbie Met James', he said: ''I think I stand somewhere just above Steps and slightly below Westlife. Not far away from there.
''I think that a lot of people don't like my brand of whatever I do. I am the quintessential boy next door, I feel that way.
''I have a gigantic ego and need to be at the top of the pile and be doing amazingly well. Also, at the same time, I'm just pleased to be anywhere.
''Do I think I'm a national treasure? I don't see why not? I don't see why I shouldn't be. I'm a good lad really.''
''When Robbie Met James' airs on Sky One on Friday (23.11.12) at 9pm.