EXCLUSIVE: Why Tyra Banks Hid Her Baby News From Her Closest Friends -- Plus, She Wants More Kids!

Find out the heartbreaking reason why Tyra Banks kept her baby news a secret even from her closest friends.

Tyra Banks couldn't be more overjoyed about her new baby boy, York Banks Asla, as it has been her "dream" to be a mother for a very long time, a source close to Tyra revealed to ET on Thursday.

The 42-year-old supermodel surprised fans when she announced she welcomed her first child, via surrogate, on Wednesday, and now we know the reason for the former America's Next Top Model host's secrecy.

"The reason she kept it so private is because the heartbreak has been so intense with many false starts and failed attempts, that she didn’t want to say anything until the baby actually arrived," the source said. "She kept the secret from even her closest friends until yesterday, and reached out to a small circle right before she announced to the world."

WATCH: Surprise! Tyra Banks Welcomes 'Miracle' Baby Boy Via Surrogate, Thanks 'Angel' Who Carried Him

And according to our source, Tyra isn't likely stopping at one child -- she definitely wants more.

The beauty entrepreneur has been open about her fertility struggles and "traumatic" experience undergoing IVF treatments in the past. Our source told us that Tyra's been trying for a year and a half to get pregnant.

"Implanted embryos weren't working for her to carry," the source said. "She has been harvesting eggs for the last 18 months to make this dream a reality."

York is the genetic son of Tyra and her boyfriend, Norwegian photographer Erik Asla, the source shared. While York is Tyra's first child, she's already been enjoying being a stepmother figure to Erik's two daughters for the past two years, our source added.

"She is great with kids and always wanted to be a mother," the source said.

Obviously, we have to admire Tyra's ability to maintain such a big secret! Tyra even played it cool over the weekend when she went to see Jennifer Lopez's "All I Have" show in Las Vegas, making no mention of her big baby news.

Instead, she Instagrammed a pic of herself and her mother trying on wigs on Sunday, writing, "When mother and daughter trade their hair..."

WATCH: Tyra Banks Reveals Her Fertility Struggles and 'Traumatic' Experience With IVF

On Thursday, sources close to Tyra's former show FABLife -- which was canceled last week -- told ET that nobody had any idea that she was expecting a new addition to her family.

"We're all talking about it now but we can't figure out how it was kept a secret," one source said of the baby news.

"Tyra is a private person," another source said. "She never talked about her personal life when she was there. She came in, did her s**t and left."

Watch the video below for more on Tyra's "miracle baby boy."