The 'Mountains' rockers were in Los Angeles last year recording their new album 'Opposites' - due for release later this month - and were taken back when the 38-year-old singer invited them to play on his solo album 'Take the Crown' as they felt he is too talented to need their ''help''.
Vocalist and guitarist Simon Neil recalled: ''The guy that produced [Robbie Williams'] album, Jacknife Lee, he's a friend of ours and he told us that Robbie had said he wouldn't mind if we played on his solo record.
''The 15-year-old in me thought it would be amazing. But then I thought, 'Why do I actually want to play on it? Robbie Williams doesn't need my help.' It was an honour to be asked, though.
''We did get the opportunity to play football at his house too, but recording got in the way. It doesn't matter what kind of music you make, if you dig football then you're alright with us.''
The Scottish trio - which also inlcudes twin brothers James and Ben Johnston - are excited for fans to hear their upcoming album after experimenting with different sounds, including a traditional mariachi band.
Drummer Ben explained to FHM magazine: ''The track 'Spanish Radio' in particular shouldn't work. It has a very strange time signature and a mariachi band on it. If we told you that, you'd think we were joking but magically, we've pulled it off.
''It's without a doubt Biffy Clyro, but, well, Mexican at the same time.''