In a heartbreaking post to Instagram, the AFL player shared a picture of his wife and her baby bump, with the words 'May 2018' engrained across the image.
However, in the caption the sportsman says one child has been diagnosed with anencephaly, a serious birth defect that results in parts of the brain and skull under-developing.
Gary writes, "[Amie] and I are over the moon to share with you all that we have been blessed twice over.
"Sadly, one of our beautiful bubs has been diagnosed with anencephaly."
Gary explains while he and Amie are excited about their news, they are also coming to terms with the sad news that the affected twin will not survive at birth.
Gary goes on to explain, 'Anencephaly is a condition where part of the brain, skull and scalp never develops.
"Ames and I have known about this since our 11-week scan, and since knowing, we've been constantly discussing what we should do, how we should tell people and if we should tell people at all.
"We come to the decision that either way, BOTH our babies are beautiful, precious human beings, with the only thing being that sadly ones life is destined to be cut short," he continued.
By making their news public, the couple hope to raise awareness for anencephaly and encourage anyone who has been affected with their own children to come forward.
"Don't be afraid to talk to us about it. That's what we want, we want people to ask questions, we want to talk about it with others. We still need questions answered as much as everyone else."
This article originally appeared on New Idea.