Gwyneth Paltrow and Chris Martin were "off and on for many years" before separating.
The former couple - who have children Apple, nine, and Moses, seven, together - announced last week they were splitting after 10 years of marriage, and insiders admit they weren't surprised by the announcement.
One source said: "They were physically separated and emotionally."
Another source added to People magazine: "They have been on and off for many years. The marriage was falling apart."
The 'Iron Man 3' star and her Coldplay rocker spouse had successfully managed to juggle their busy careers and family life but friends say it was impossible for them to keep maintaining a balance.
A source said: "They seemed to have a pretty mature handle on that crazy rotation of being superstars and parents. But that balance, given the time they had to spend apart, clearly couldn't sustain itself."
And another friend thinks Gwyneth and Chris' different personalities also played a part in the problems with their marriage.
The insider explained: "[Chris] is the kind of person who is always in a T-shirt. She's much more glam."
Despite their split, the pair have vowed to stay friends for the sake of their children and are currently enjoying a family vacation.
Tagged in Chris Martin Coldplay Gwyneth Paltrow