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The singer, songwriter and actor has now opened up in his new book, "Hindsight: & All the Things I Can't See in Front of Me," about the moment he first learned he was going to be a father.
"I was on the 20/20 Experience Tour when my life changed forever," Timberlake wrote in an excerpt from the book published by E News.
Timberlake, 37, was performing at a tour stop in Detroit while Biel was in Los Angeles at the time. He received a message from her after the show.
"There was a text from Jess, in all capital letters,'' he writes. "It read 'Call Me Now.' I FaceTimed her back immediately. She answered with this look on her face, and I knew exactly what she was going to say.
"Instead, she just held up the pregnancy test, and we both started bawling. I ended the tour early so I could be at home and take care of my family."
It was a whirlwind time for Timberlake as he finished up the tour and started a new chapter in his life.
"My last show was in Las Vegas, on January 2, 2015,'' he wrote. "Three months later, I was a father."
The family also had some fun dressing as Lego characters for Halloween on Wednesday night, with little Silas as Batman.
Timberlake also writes in his new book about the origins of how he fell in love with Biel, and what he has learned from becoming a father.
"It's made me look at relationships in a new way,'' he wrote. "It's made me think about who my parents are as people, and how that affected me then and has contributed to who I am now - and how all that might affect my child.
"It makes me wonder how my son will see me when he grows up. It makes me want to be more thoughtful."
"Hindsight" is available for order on Amazon.
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