This article originally appeared on People. For more stories like this, visit people.com.

By PEOPLE.COM/Charlotte Triggs
Sep 26, 2018 @ 2:30 pm

Gisele Bündchen is known for her incredible body.

Her big break came in 1997 when she walked topless in Alexander McQueen’s runway show. She appeared on the cover of Vogue the next year as the exemplar of “the return of the curve.” Credited with ushering in a sexy, athletic look that replaced ’90s heroin chic, Bündchen became known in the fashion industry as “the boobs from Brazil” and earned a record $25 million contract for Victoria’s Secret.

But nearly 20 years later, after breastfeeding Benjamin and Vivian, her children with husband Tom Brady, for more than 18 months each, Bündchen says her self-esteem took a hit when she realized her breasts were now smaller than before — and slightly uneven.

“I was always praised for my body, and I felt like people had expectations from me that I couldn’t deliver,” Bündchen, 38, says in a revealing interview in this week’s issue of PEOPLE, on stands Friday. “I felt very vulnerable, because I can work out, I can eat healthy, but I can’t change the fact that both of my kids enjoyed the left boob more than the right. All I wanted was for them to be even and for people to stop commenting on it.”

In a new memoir, Lessons: My Path to a Meaningful Life, the famously private Bündchen reveals that in 2015, she discreetly went under the knife for a breast augmentation — a decision she says she immediately regretted.

“When I woke up, I was like, ‘What have I done?’ I felt like I was living in a body I didn’t recognize,” she says. “For the first year I wore [baggy] clothes because I felt uncomfortable.”

Bündchen says her husband, Patriots quarterback Tom Brady, 41, was a source of support.

“He just said, ‘I love you no matter what’ and that I looked beautiful,” she says. “This was definitely another lesson: What doesn’t kill you makes you stronger. But I wish I would have learned that a different way.”

For more on Bündchen’s book, pick up the current issue of PEOPLE, on stands Friday. 

In her candid new memoir and interview with PEOPLE, Bündchen also opens up about battling panic attacks and suicidal thoughts, as well as the stresses of marriage and motherhood.

RELATED VIDEO: Gisele Bündchen Is Writing a Book About Modeling, Marriage and Leading a ‘Meaningful Life’

“Things can be looking perfect on the outside, but you have no idea what’s really going on,” says the mother of Benjamin, 8, and Vivian, 5. (Bündchen is also close with Brady’s son Jack, 11, with actress Bridget Moynahan, whom she calls her “bonus child.”)

“I felt like maybe it was time to share some of my vulnerabilities, and it made me realize, everything I’ve lived through, I would never change, because I think I am who I am because of those experiences,” Bündchen says.