Biel, 38, is said to have given birth to a son earlier this week and is reportedly recovering with her husband Timberlake, 39, eldest son Silas, 5, and their new baby.
Biel’s mother Kimberley is also with the family, a friend reportedly told MailOnline.
The celebrity couple have not been pictured together in public since March and are thought to be living in their remote Montana home.
Timberlake posted a photo to Instagram on March 25 that shows Biel standing in a snowy, mountainous valley.
The couple’s relationship has recently been rocked by infidelity allegations after Timberlake was seen getting close to a fellow actor.
He was seen holding hands with Alisha Wainwright during filming for NFL film Palmer late last year.
Two weeks later, Timberlake apologised to Biel on Instagram and admitted to drinking too much that night.
He said: “I stay away from gossip as much as I can, but for my family, I feel it is important to address recent rumors that are hurting the people I love.
“A few weeks ago, I displayed a strong lapse in judgement – but let me be clear – nothing happened between me and my co-star.
“I drank way too much that night and I regret my behavior. I should have known better. This is not the example I want to set for my son.
“I want to apologize to my amazing wife and family for putting them through such an embarrassing situation, and I am focused on being the best husband and father I can be.
“This was not that. I am incredibly proud to be working on Palmer. Looking forward to continuing to make the movie and excited for people to see it.”