While the couple were on a break, he fathered a son with "Basketball Wives" star, Aja Metoyerin, in 2013.
Dwyane Wade said telling his wife he fathered a child with another woman while they were on a break was the biggest challenge of his life.
The NBA great opened up about letting Gabrielle Union know he welcomed Xavier, six, with "Basketball Wives" star, Aja Metoyerin, in 2013 while the couple were estranged and shortly before he proposed to Union.
"I had a child with someone else and I had to tell her. Hardest thing I've ever had to do is man up and tell Gabrielle Union that I've had a child with somebody else," he said in his upcoming ESPN documentary "D. Wade: Life Unexpected," according to ET. "I couldn't sleep. I wasn't eating."
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"When you hold something in that you know is going to come out and you have this information and you know it's gonna f--k somebody's life up, that you care about, that you love, if it don't hurt you, then you're not human," Wade continued.
"Me and Gab just went through something that you never want to go through and we still came out of it."
Wade was already dad to Zaire, 18, and Zaya, 12, and guardian to nephew Dahveon, 18.
The basketball legend and Union married in 2014. "She wasn't just marrying me, she was marrying all this baggage," he said of including his kids in the proposal, according to the outlet.
They welcomed daughter Kaavia via surrogate in 2018.
At the premiere of the documentary, Wade opened up about the couple's struggle to get pregnant and the challenge of raising his daughter Zaya, who was born a male.
"We're not the only family that deals with all the things we've spoken about. We're not the only family that had to deal with surrogacy, to bring our daughter into the world," Wade told ET. "We're not the only family that's had to deal with gender expression, gender identity, sexuality, with their child."
"We understand the position we've been put in, especially in our community, and even though it's not always a popular thing to speak out on issues that people are uncomfortable with or not as educated on," Wade continued. "But this is the platform that God gave me and my family, so we use it."
"D. Wade: Life Unexpected" debuts on ESPN on Sunday, February 23 at 9 p.m. ET/PT.