Gwen Stefani admits marriage to Gavin Rossdale was in trouble before birth of 20-month-old son Apollo

Gwen admits the split was a long time coming

Gwen Stefani and Gavin Rossdale's marriage was on the rocks before the birth of their 20-month-old son, Apollo.

The Voice mentor, who filed for divorce from the Bush frontman in August after 13 years of marriage, admits she went through "hard times before the baby, personally" last year and credits her role as a mentor on the show for giving her a new lease of life.

The 46-year-old star, who also has sons Kingston, nine, and Zuma, seven, with her estranged husband, said: "I got so much out of that first season that I didn't expect, creatively, from being around so much music.

The pair were married for 13 years

There were hard times before the baby, personally, that were just not good. And then having Apollo, and being on the show, and being refreshed - it was just like, Whoa!"

"Filming the show... was so amazing. I cried every day I was there. It was so intense. But I'm in a really positive place now."

Gwen, who recently started dating her fellow mentor Blake Shelton , walked down the aisle with Gavin, 50, in 2002 in a pink ombré Christian Dior gown but recently began clearing out her closet.

Gwen is now dating her Voice co-mentor Blake Shelton

Nudging a large white box with her toe, the blonde beauty told the December issue of InStyle magazine: "That's my wedding dress."

But there are some items the No Doubt star would never get rid of, including a slouchy pair of Comme des Garçons trousers.

She added: "Being able to wear couture clothes is really special. These are works of art, and I get to play around like I'm a big Barbie."