The Irish rocker and the 'Let Me Entertain You' hitmaker have kept a close eye on one another over the years as they've both battled with depression and addiction, in order to not let their self-admiration get the better of them.
When the 'Get Out of Your Own Way' singer's bandmate The Edge said: ''He used to take care of Robbie Williams so he didn't do anything stupid'', Bono agreed: ''I am Robbie Williams.''
Speaking about the lyric, 'I lie for a living' on U2's song 'The Showman' from their latest record 'Songs of Experience', which is about how showmen can disguise feelings through humour, the group's frontman said: ''When you watch U2 shows in the 80s and especially in the 90s there was always a lot of humour.
''I think it is important to show the other side as well.
''But just because 'The Showman' is humorous does not mean it's less meaningful.
''I'm talking about performers and how to be aware of them; they can pretend to do anything - cry, laugh, even have an orgasm.''
Asked if playing to Stadium-sized crowds - which they will tour on the 'eXPERIENCE & iNNOCENCE Tour' later this year - engages his ego, Bono told the Daily Star newspaper: ''You would expect it to if you are standing in front of 70,000 people every night.
''But the exact opposite is the case.''
Guitarist The Edge - whose real name is David Evans - agreed: ''The ego implodes.''
And Bono added: ''My ego is smaller a the end of a U2 tour than at the beginning.''
On/off Take That star Robbie previously revealed at the height of his drug addiction, he took magic mushrooms at Bono's house, and was so high he thought a window was ''the best painting'' he'd ever seen.
He recalled: ''I remember a great psychedelic time - by psychedelic I mean mushrooms.
''I arrived at Bono's house, let's say I was already elsewhere.
''I was looking at the best painting in the world I had ever seen.
''My mouth dropped to the floor, thinking 'Wow, Bono has the best painting I have ever seen...'
''Then Bono appeared. I told him, 'Hey, you got the best painting I have ever seen, and Bono said: 'Robbie, You're looking at the window.'''
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Sometimes actors are not acting.