Gisele Bundchen felt like her "world turned upside down" when she learned Tom Brady was having a baby with ex Bridget Moynahan.

The supermodel got extremely candid in a new excerpt from her book "Lessons: My Path To A Meaningful Life".

Brady told her Moynahan was expecting when he and Gisele had been dating for just two months - though Gisele never refers to her by name in the book, reports the Daily Mail.

"Two months into our relationship, Tom told me his ex-girlfriend was pregnant. The very next day the news was everywhere, and I felt my world had been turned upside down," writes the retired Victoria Secret Angel.

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Gisele had been blindsided.

Before his relationship with the catwalk queen, he dated model Bridget from 2004 to 2006. She got pregnant in November or early December.

Gisele says she met Tom on a blind date in December 2006. Jack was born in August 22, 2007.

And while the public scandal over Bridget's pregnancy "wasn't an easy time" for Bundchen or Brady, the model said her NFL quarterback love "especially" needed support at the time.

"I wanted to be there for Jack and Tom, and do whatever I could to create stability in their lives, and help them to have a close relationship."

Though rattled by the drama, the Brazilian beauty revealed how Brady and Bridget's son John, who goes by Jack and now 11, was a blessing in disguise, crediting the little one with helping her "heart expand in ways I didn't know was possible."

She also revealed how she refers to Jack as her "bonus child" and how his birth inspired her and Tom to have children of their own sooner than they necessary would have, so that the siblings would be close in age.

The couple have an eight-year-old son named Benjamin and a five-year-old daughter called Vivian.

Gisele credit's Jack's birth with accelerating Tom growing up and shifting their priorities.

When Tom needed surgery in 2008, he got it in LA to be close to his son.

And now the family and half siblings are so close to Jack that often after dinner in Boston, they Facetime with Jack. They check on how he's doing and say goodnight.

She says that when he's visiting, Jack "takes his older-brother status seriously" and is an excellent soccer player and skier.

She also revealed that her stepson "bonus child" is learning her native language of Portuguese. Benjamin and Vivi are fluent, and Jack is now speaking it "more and more" and his accent is "so cute".

As her parents and family don't speak great English, it is important to Gisele that her kids can communicate with them

Gisele shared several other honest moments from her tome during a sit down with Good Morning America's Robin Roberts on Tuesday.

She told the AM show anchor that she hit "rock bottom" when she started wrestling with panic attacks in her twenties, and how she experienced her first episode while flying on a six-seater plane and getting caught in some turbulence.

"That was definitely rock bottom for me," Gisele said of the period of her life that was impacted by the anxiety attacks.

"It started all in a little plane. I was in Costa Rica and I was flying a six-seater plane and the plane started shaking like a little leaf. I was, like, completely a sense of powerless(ness), you know?

"I'm the kind of person who likes to have things under control. That was definitely an out-of-control moment and it kind of started this kind of fear of being in small spaces."

Gisele's anxiety grew from there until it started having an impact on her daily life.

"So it started with a little plane ride but then it became tunnels, subways, elevators," the model added during the interview, which took place at her home in Brookline, Massachusetts.

"I lived on the ninth floor in an apartment and I would go up nine floors of stairs because I was scared that I would suffocate. It was crazy. My world just kept getting smaller and smaller."

On Tuesday morning, she became emotional as she talked about that point in her life, and had to compose herself before telling Robin through tears: "The reason why I wanted to share this story that to me is very private and puts me in a very vulnerable position in a way is with the hopes that people don't feel alone.

"It was like I was trapped and I couldn't breathe even outside on my own balcony. From that moment on, I realised that my life needed to change."

The model went to see a specialist who gave her a prescription for Xanax, but Gisele feared the idea of being "depending" on medication.

She eventually changed her lifestyle completely with the guidance of doctors, turning to yoga and meditation as well as changing her diet.

"I had been smoking cigarettes, drinking a bottle of wine and three mocha Frappucinos every day, and I gave up everything in one day," she told People.

"I thought, if this stuff is in any way the cause of this pain in my life, it's gotta go."

In 2005, Gisele also broke up with Leonardo DiCaprio, whom she had been dating since 2000, after doing some soul-searching.