Jenna Dewan felt "blindsided" when Channing Tatum began dating Jessie J and she read about the romance online.
The "Step Up" actress - who is expecting her first child with boyfriend Steve Kazee - filed for divorce from the "Magic Mike" actor in October 2018, citing irreconcilable differences, and was later shocked to learn online that he'd moved on with the singer.
She revealed: "I was learning things about my ex most people wouldn't have to face-and over the internet, as it was happening.
"There I was, on a plane, alone, finding out about his new relationship. I felt blindsided. Choosing grace as I learned everything about my personal situation along with the rest of the world was really difficult
"It was quite a challenge to remain graceful; to say the least. That's when your real character comes out. Instead of reacting the way I wanted to...I asked myself this: How do I choose grace in this moment? Had I not been practicing this way of life beforehand, I definitely wouldn't have handled this news very gracefully."
The 38-year-old star - who has six-year-old daughter Everly - with Channing - felt like she'd been hit by a "tumbling avalanche" in the wake of her marriage ending and admitted it was a very "testing" time.
Writing in her new book, "Gracefully You: Finding Beauty and Balance in the Everyday", she recalled: "In the beginning of my separation, it felt as though I were in a dark closet, desperately trying to find the light or the way out. I was in a state of shock.
"One week I'd be doing really well and the next I was slammed with a whole new slew of emotions.
"The rumour mill was churning out story after story. There were many times I hid under the covers, wondering what was next.
"The pain hit me like a tumbling avalanche. I was completely overcome with fear and sadness. It took many moments of sitting alone with my grief to force me into surrendering to my roller coaster of a situation.
"The separation tested me in ways I hadn't thought possible. I started to wonder if everything I believed in and always talked about was real. Could anyone or anything ever be trusted?"