Jack has been Chris Pratt and Anna Faris’ main focus since the former couple split.

By Char Adams and Kate Coyne
October 19, 2017
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This originally appeared on People.com.

and ‘s 5-year-old son is a healthy little boy today. But there was a time when the proud parents were unsure of their son’s fate.

In her revealing new memoir , the 40-year-old actress and the “emotionally exhausting” weeks that followed, in which she and now-ex Pratt worked to come to terms with terrifying news.

“The pediatric neurosurgeon sat Chris and me down to tell us that Jack had some severe brain bleeding and there was a chance that he could be developmentally disabled,” Faris writes of Jack, who was born .

“I was in complete shock … So Chris and I did what we could, which was hold hands and hope and face it together,” adds the  star.

Doctors told the parents that they would not know for sure until Jack was about 18 months old whether he would have special needs. Faris had been on bed rest for about a week before .

As doctors swarmed and she confronted the pain of not knowing when she’d get to hold her baby, Faris says her mindset became, “I have to be as … I have to.”

But the hardest moments for the couple came after the birth, as Jack was poked and prodded in the neonatal intensive care unit for weeks.

“These moments can be hard on couples, but for us it really brought us together,” she writes. “It felt like it was .”

About a month later, Faris and Pratt, 38, got to home. And in the years that followed, the little boy would grow healthy with only slight vision and leg muscle issues.

“Today, Jack is at a beautiful age. He has some temper tantrums occasionally (did I mention he’s 5?) but he’s a really good kid and delicious and likes cuddles,” the proud mom continues.

Jack has been Pratt and Faris’ main focus since ; they announced the breakup in August. Now, she tells PEOPLE that she’s grateful for Pratt and their greatest treasure: Jack.

“We have the most together,” Faris says.

 is available starting Tuesday.

For more about Anna Faris’ soon-to-be-released memoir, pick up the latest issue of PEOPLE, on newsstands Friday.