The Coldplay frontman and the 'Iron Man' actress - who have children Apple, 14, and Moses, 12, together - announced in 2014 they had gone their separate ways after 10 years of marriage and the 41-year-old singer admitted he reached a low point while the group were touring their 'Mylo Xyloto' album.
He said: ''Through the course of the next album 'Mylo Xyloto', it was pretty clear that I was doing well in some parts of my life and really not well in others.
''When we're on tour, it's just a little bubble, you become institutionalised. And this is why a lot of frontmen have problems in their personal lives.
''Towards the end of the Mylo tour, it was a very difficult period for about a year or so of feeling completely worthless and nothing to anybody.
''I was just like, 'I'm a mess', really, because I can't enjoy the great things around me.
''Then, of course, I went through a break-up with Gwyneth.
''Listen, I'm never going to moan, I'm grateful for everything, but it was pretty touch and go.''
Phil admitted: ''Your mind can go to the worst case scenario. 'I was worried about him to the extent that I was just really glad to get a text in the morning just to know he was OK.''
Will said: ''It was evident that things were very difficult for Chris and that he was unhappy.
''We sort of felt helpless in a way. Naturally it's distressing when your friend is going through something so traumatic.''
Despite their global success, Chris - who is now in a relationship with Dakota Johnson - lacks confidence in himself and the band's musical output.
Speaking in upcoming documentary 'A Head Full of Dreams', he said: ''I think everything we've done is s**t. That's why I keep trying to do new stuff. But that's my gut feeling. That's what fires you up to do the next thing.''
And the 'Viva La Vida' hitmaker doesn't mind when people mock the band.
He said: ''I get it. I think it's important to have figures of ridicule and I don't mind being one of them.''
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