Gwen Stefani - mom, fashion designer, and rock star - turns the big 4-oh! today. See photos of the pop star after the jump...

The singer has admitted the hardest thing she's ever done is have children. She is mom to Kingston, three, and Zuma, one. "Everything from getting up in the morning to trying to be consistent to trying to have the right feelings. But, of course, the rewards are so great," she told Glamour.

Gwen recently lamented the fact that she was a bad student in school. She admitted she is still haunted by her fear of exams because she was convinced she was talentless.

She said, "I never had any kind of ambitions. I just thought I was going to have babies... When I found out that I could write songs, I felt like all of a sudden I'd found myself. Like, really, this power that I had that I never had before. It was amazing to have something that I could do after the whole school problem."

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