has revealed a heartbreaking loss.
In a joint Instagram post with wife Kelsey Henson on Instagram Friday, the alum, 34, and his wife, 33, shared they have experienced a pregnancy loss.
Sharing of their brief time with daughter Grace Morgan Hafthorsdottir, they explained the circumstances in a lengthy caption.
"It is with great sorrow that we announce the birth of our daughter, Grace Morgan Hafthorsdottir, born Nov 8th at 21 1/2 weeks gestation. After a noticeable decrease in movement we found out her heart had stopped beating," they wrote.
"Words cannot describe our pain of this loss or our happiness at being able to spend time with our daughter. She is absolutely beautiful, with blonde lashes and brows and a little smile for mom and dad. The love we feel for her is overwhelming," the caption continued.
"The grief we feel will be with us forever but so will the love. All of our hopes and dreams for her have been taken away from us but I know I will be with her again. Her spirit lives on through us and her siblings. We ask that you respect our privacy at this time as we grieve this unbearable loss. Thank you all for any kind words and support."
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The couple's son Stormur, 3, — who is seen with baby Grace in the photos — was at the center of the couple's pregnancy announcement last month.
In the photos, the actor posed next to his wife, who wore an open white shirt showing her baby bump. Stormur stood in front of them, holding up a sonogram strip and wearing a black T-shirt that read "brother."
"Life is precious and I couldn't be happier to announce that our family is growing bigger," Björnsson wrote in his caption. "Kelsey is 19 weeks pregnant with a healthy child who we cannot wait to meet!"
In addition to son Stormur, Björnsson also shares daughter Theresa Líf with ex-girlfriend Thelma Björk Steimann.
The star and Henson in his native Iceland.