Fergie and Josh Duhamel have been "leading separate lives" for a long time.
The pair announced they were separating earlier this week after 13 years together but the split had been on the cards for a long while.
A source told People magazine: "They have been leading separate lives for a long time. She wants to be out on the road doing her thing, while he is more chill. They clashed for a long time before they did anything about it."
In a statement, the former couple expressed their desire to keep their split as much of a "private matter" as possible.
They said in a statement: "With absolute love and respect, we decided to separate as a couple earlier this year. To give our family the best opportunity to adjust, we wanted to keep this a private matter before sharing it with the public. We are and will always be united in our support of each other and our family."
Meanwhile, Fergie's mother recently admitted she didn't know the singer had split from Josh.
Terri Jackson said at the time: "What? This is the first I'm hearing of this. I don't get it. I was there [at the party last week]. They seemed happy."
Meanwhile, Josh previously admitted he doesn't want to "screw up" his son and praised Fergie for being much more "patient" with their four-year-old son Axl than he was.
He said back in June: "She's definitely more evolved than I am, and more patient. Having a kid at 40 years old is much different than having one at 22, you know, so I'm a little more mature than I was then. I'm just doing the best that I can, trying not to screw him up for life. You never know."