"We are shocked and in the kind of deep pain you only hear about, the kind of pain we've never felt before," she wrote in an Instagram post. "We were never able to stop the bleeding and give our baby the fluids he needed, despite bags and bags of blood transfusions. It just wasn't enough."
While Teigen noted she and Legend waited "until the last possible moment" to name their children, Luna, 4, and Miles, 2, she wrote they had already "started to call this little guy" Jack.
"So he will always be Jack to us," the Chrissy's Court star continued. "Jack worked so hard to be a part of our little family, and he will be, forever. 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."
Legend, who announced the pregnancy with Teigen in his "Wild" music video back in August, posted a tribute of his own on Twitter. Alongside five hearts, he wrote, "We love you, Jack."
After Teigen shared her devastating news, several stars rallied around her family with words of support. Scroll on to read their messages.
Mariah Carey: "I'm so sorry. I love you. Here for you if you need to talk."
Kim Kardashian: "We're always here for you and love you guys so much."
Hailey Bieber: "I'm so so sorry. Thinking of you and John, praying for you guys and sending you so much love during this time."
Paris Hilton: "My heart breaks for you and John. I am so sorry for your loss. Sending you and your family so much love. Love you beautiful."
Gabrielle Union: "We love you guys so much and we will be here for whatever yall need. Always."
Channing Tatum: "Sending so much love to you right now."
Jesse Tyler Ferguson: "Sending so much love to you and John and the kids. I wish I could take away your heartbreak."
Charlie Puth: "We love you and are here for you and your family."
Nicole "Snooki" Polizzi: "I am so sorry! Praying for you and your beautiful family."
Selma Blair: "I am so sorry angel momma. I am so sorry. This grief. This grief. It will hold you and the love will break through. I am so sorry. Your family. [Heart] You. Love you. My deepest sympathies."
Viola Davis: "So very sorry Chrissy and John. A big virtual hug of love, love, love…and more."
Malika Haqq: "May the love in your hearts be healing over your beautiful family. God bless you guys."
Ruby Rose: "Thinking of you. I'm so sorry."
Cara Delevingne: "Sending you and John so much love. X."
La La Anthony: "Sending so much love and prayers to you, John and the family. My heart goes out to you. Praying for peace and healing."
Dwayne "The Rock" Johnson: "We are so deeply sorry and sending you guys all our love, strength, support, light and mañana. No more words. D&L."
Dove Cameron: "My whole heart is throbbing and aching for this pain. I am so sorry. I am holding this in my body tonight. You are never alone."
Sophia Bush: "Oh sweetheart. I am so so sorry. Holding your hearts in my heart."
Aaron Paul: "I love you."
Chloe x Halle: "We are so so sorry. Praying for your beautiful family and sending love. God bless you."
Naomi Campbell: "I'm so sorry for your loss Chrissy & John, you bring us so much joy and laughter, we are here for you through this difficult time."
Todd Chrisley: "We love you sweet girl. Our prayers are always with you and your beautiful family, May God lift you up during these confusing times."
NikkieTutorials: "I am so sorry. We are all here for you!!!"
Busy Philipps: "I'm so deeply sorry for your immeasurable loss. In awe of your bravery and selflessness in sharing as you have, which is going to help so many women and families. Sending you and your family all the love and light while you grieve."
Alyssa Milano: "Thank you for sharing this. I'm sending you all the love and strength. I'm so sorry."
Kyle Richards: "Chrissy and John, I am so so sorry to hear this news. Sending you all love. Will say a special prayer for Jack tonight. Your guardian angel."
Josh Gad: "I am so truly sorry. My deepest sympathies and prayers are with you, John and the whole family. You are surrounded by love and light."
Vanessa Lachey: "Babe, I'm so sorry. Sending Love & Light."
Olivia Culpo: "I'm so so sorry Chrissy :( Sending love, prayers, and positive energy your way."
Jenna Dewan: My whole heart to you and John during this time."
Skai Jackson: "So sorry for your loss. Jack will always be with you."
January Jones: "I'm so so sorry. This is heartbreaking, sending love."
Michelle Williams: "Chrissy and John, I am so so sorry!!!"
Olivia Munn: "I'm so so sorry. Sending all my love."
Bethenny Frankel: "It's impossible to assign words to this pain and tragedy. It's the sad storm you weather while holding your babies and family and pray for the sun to shine again. XO."
Hilary Duff: "Rest mama. Sending you mountains of healing love to you and your beautiful family. Jack will forever be your family's angel. So sorry."
Khloe Kardashian: "I am so so sorry!!! You and John know my family and I are ALWAYS here for you and yours FOREVER!! We love you all so much."
Elizabeth Banks, "Deepest sympathy to your family, sending light and love."
Jeremy Renner: "I'm so sorry. I love you."
Cassie: "Sending all my love and prayers to you, John and your babies. I pray for your healing."
Andy Cohen: "Sending you love."
Kate Upton: "I'm so sorry! Praying for you guys and sending you so much love!"
Julianne Moore: "I'm so sorry for your loss."
Simone Biles: "Sending love."
Erin Andrews: "I'm so sorry Chrissy. So Sorry."
Ashley Tisdale: "Sending you so much love and prayers."
Michelle Pfeiffer: "I am so sorry for your loss. Sending love."
Zelda Williams: "However someone chooses to grieve, publicly or privately, is VALID. Grief will fill a room if you let it, and spill out of every window and door. Let people grieve however they choose, not however you believe they should, and hope the world returns the favor for you one day."
Demi Moore: "Sending so much love."
Mandy Moore: "Sending you and your family all the love and space to grieve and heal. You are such a fighter, as was Jack."