"Bachelor" alum Sarah Herron shared the devastating news that her son, Oliver Brown, was born prematurely at 24 weeks on Tuesday and "passed away in his dad’s arms shortly after."

"There are no words for the magnitude of loss and pain we’re experiencing. It’s beautiful and simultaneously tragic. He had my nose and his dad’s mouth and long fingers," she wrote in an Instagram post Wednesday, along with a photo of her baby lying on her chest and her fiancé, Dylan Brown, kissing her forehead.

Herron called Oliver an "IVF miracle," saying that he had "defied so many odds and fought through so many hard milestones to be here, but the higher powers still had other plans for the three of us."

The 36-year-old, who was on the reality show in 2013 when Sean Lowe was the bachelor, announced her pregnancy last September. 

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Sarah Herron smiling

Sarah Herron announced her pregnancy in September. (Amanda Edwards / Getty Images / File)

She continued, "Our time together was short, but we are grateful for the days we had with Oliver in my belly. He has taught us so much about the integrity of life, love and death. Oliver filled our home and hearts with so much love and most importantly, optimism. The stars aligned to create Baby Oliver with a deep, meaningful purpose bigger than we’ll ever understand. His body was small, but his legacy will always be larger than life to us."

Herron remembered that while she was pregnant her baby swam with sea turtles, kept her company when she recovered from knee surgery, loved his dad’s cooking and lying with their dog, Rio. 

A carousel of photos from Herron’s pregnancy echoed those memories and also included a photo of a Christmas ornament on their tree that said, "Oliver 2022." She also included a heartbreaking photo of her fiancé comforting her while she cried in a hospital bed.

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"While our hearts are shattered beyond comprehension, we are comforted knowing that our son’s soul only ever knew love and will not suffer in a body that wasn’t built for this life," she added.

Sarah Herron with fiancé Dylan Brown

Sarah Herron said their son died in fiancé Dylan Brown's arms. (Amanda Edwards / Getty Images / File)

She concluded her note by writing, "We’ll never understand the cruelty of it all, but through the darkness, Oliver remains so so bright. We love you so much, baby boy. You will never be replaced. You are so perfect and awesome."

The note was signed, "Love, Mommy and Daddy."

Sarah Herron in a red dress

Sarah Herron said her son, Oliver, was born prematurely at 24 weeks old. (Allen Berezovsky / WireImage for Fashion Media / File)

Bachelor Nation flooded the 36-year-old with well-wishes.

Emily Maynard wrote in part, "Oh sweet Sarah. I’m so sorry. I truly have no words. Oliver will remain a shining light in this world for you and Dylan."

Former "Bachelor" host Chris Harrison said, "God bless you all Sarah. We love you."

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Catherine Giudici, who met and married Lowe on the "Bachelor," said she was "Sending you so much love and praying for you both right now."

In her Instagram story Thursday, Herron said that she had read all of the more than 8,000 messages of support overnight: "It helps to hear your stories," she wrote, along with a photo of Brown and Rio asleep in the living room.

Another photo showed Rio cuddled up with a teddy bear.

Rio snuggling teddy bear

Sarah Herron wrote in her Instagram story that their dog, Rio, had fallen asleep with a teddy bear from their late son's bassinet. (Sarah Herron / Instagram)

"The hospital gave us the teddy bear that was in Oliver's bassinet," she wrote. "The teddy's fur is almost identical to Rio's color. We gave it to him as soon as we got home and Rio didn't try to chew it or destroy it, he just slept with it tightly under his chin. His baby."