At the height of their fame, one Destiny's Child star was secretly suffering dark thoughts.

Michelle Williams was one-third of one of the most successful girl groups of the early noughties.

Together with Beyoncé and Kelly Rowland, Michelle and Destiny’s Child won countless Grammy, American Music, Billboard and BET awards and sold more than 60 million records.

But while singing pop and R&B hits like Say My Name, Survivor and Bootylicious, Michelle has revealed she was struggling with a deep and dark depression.

"I'm in one of the top-selling female groups of all time, suffering with depression," she said while co-hosting US talk show The Talk.

"When I disclosed it to our manager [Beyoncé's father, Matthew Knowles] he was like, 'Y'all just signed a multi-million dollar deal, you're about to go on tour, what do you have to be depressed about?'

"I was like, maybe I'm just tired."

It wasn't until things got "really, really bad" that Michelle - now 37 - realised she was suffering from mental illness.

"I was suicidal...I was in that place where it got so dark and heavy... I wanted out," she said.

Michelle also revealed that she believed she had been struggling with depression since she was just 13, but never knew there was a name for what she was feeling.

"I didn't know until I was in my 30s what was going on," she said.

"I thought it was growing pains, I just thought I was turning into a woman."

The singer wants to share her story to "normalise" the discussion around mental health.

"So many people are walking around acting like they've got it all together, and they're suffering," she said.

If you or someone you know needs help you can call Lifeline on 131 114 or Beyondblue 1300 224 636.

LISTEN: Does the media have a responsibility to report on suicide?