NFL player Ryan Kelly has announced that his baby daughter has tragically passed away.

Kelly - who plays as a center for the Indianapolis Colts - announced the news on Instagram, alongside his wife, Emma. The heartbroken parents revealed that daughter Mary Kate had suffered heart failure halfway through the pregnancy.

Per People, the couple spent 48 hours in hospital, with Emma enduring 24 hours of labor. In a post of her own, Emma announced that she gave birth to Mary Kate on December 17.

In an emotional Instagram post, Kelly wrote: "Nothing made me happier than being your Dad. You gave your Mom and I that gift. You were simply a miracle and always will be.

"I’m sorry you never got to open those sweet eyes and see us or take your first steps but you have angel wings now. You left this world too soon but we know God had a bigger purpose for you.

"Your mom and I find comfort knowing you’re being loved on by your great grandparents. Thank you for watching over us and your future siblings. I’ll forever wonder who you’d be today. Until we meet again my sweet girl, I love you."

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Kelly shared a series of images, including one of Mary Kate's handprint and another of the couple looking down at their daughter.

In her own Instagram post, Emma wrote: "Please understand this post is necessary for us, so that we may begin our healing and accept our new reality."

She continued: "There is no easy way for us to say what we’re about to say... but we lost our sweet baby, Mary Katherine Kelly, aka Mary Kate, this week. I was 19 weeks along, 1 week from the halfway mark. Women have a 1% chance of losing their baby this far along, and yet somehow, here we are.

"One of our Angel nurses, Kalyn, told us this would be the hardest thing we’ll ever do in our life, and I pray to God she’s right. Because this feels worse than hard, it feels so evil and cruel. The pain and brokenness is so unbearable for Ryan and I we don’t even know where to begin."

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Emma added that "for reasons unknown", Mary Kate's heart stopped on Wednesday afternoon.

"After learning she wasn’t with us anymore, I was told there was no other choice but to deliver our baby next," she writes, adding: "I was so angry at first that I had to deliver her, only for it to become the biggest blessing out of this nightmare. It gave Ryan and I the opportunity to hold our little Saint, Mary Kate, before officially saying goodbye to her."

She went on to thank the "army of people" who are helping the couple through this heartbreaking time.

Understandably, Kelly missed his scheduled Week 15 game against the Patriots on Saturday. His team went on to win 27–17 despite his absence.

Our thoughts go out to Ryan, Emma, their family and friends, and anybody else affected by this heartbreaking news.

Featured image credit: PA Images / Alamy

NFL star Ryan Kelly announces heartbreaking death of baby daughter Mary Kate