Chrissy Teigen and John Legend have lost their unborn baby boy, whom they had named Jack, to pregnancy complications.

Chrissy Teigen, who had been admirably open about her difficult pregnancy journey, wrote a heartbreaking tribute for her unborn child and shared it on her social media accounts on Wednesday night.

Alongside a series of devastating pictures from her hospital bed, including one that showed her and John Legend weeping as they held Jack swaddled in a blanket following the miscarriage, the 34-year-old wrote: "We are shocked and in the kind of deep pain you only hear about, the kind of pain we've never felt before."

The cookbook author, who was admitted to the hospital over the weekend after experiencing heavy bleeding, revealed that they were "never able to stop the bleeding and give the baby the fluids he needed, despite bags and bags of blood transfusions."

"It just wasn't enough," she wrote.

The model, who shares two children with the musician- daughter, Luna, four, and son Miles, two, further shared that this was the first time they named their baby before birth. Both their children were born via IVF after they struggled to conceive naturally, but this time Teigen was able to fall pregnant without treatment.

She wrote: "We never decide on our babies' names until the last possible moment after they're born, just before we leave the hospital. But we, for some reason, had started to call this little guy in my belly Jack."

"So he will always be Jack to us. Jack worked so hard to be a part of our little family, and he will be, forever," the mother-of-two added.

In a special message for her lost son, the television presenter wrote: "To our Jack - I'm so sorry that the first few moments of your life were met with so many complications, that we couldn't give you the home you needed to survive. We will always love you."

Chrissy also expressed gratitude to her family and her supporters for sending "positive energy" during these trying times for the couple and said they are grateful for the life and the two "wonderful" babies they have. "But everyday can't be full of sunshine. On this darkest of days, we will grieve, we will cry our eyes out. But we will hug and love each other harder and get through it," she concluded.

John Legend and Chrissy Teigen
John Legend and Chrissy Teigen married in September 2013 REUTERS/Mario Anzuoni

Around an hour after her announcement, Chrissy took to Twitter to give an update on her situation and appeared heartbroken with her tragic loss. She wrote: "Driving home from the hospital with no baby. How can this be real."