Dwyane Wade opens up about difficult time in relationship with Gabrielle Union: "I had a child with someone else and I had to tell her"

Dwyane Wade seems to be an open book lately — even if it is difficult to reveal some of the chapters of his life. In a new ESPN documentary, "D. Wade: Life Unexpected," the former NBA star speaks about a challenging time in his life: telling his then-girlfriend, Gabrielle Union, he'd fathered a child she didn't know about. 

Wade and Union began dating in 2008. But the NBA star fathered a child with someone else in 2013, when he and Union were on a break, according to Entertainment Tonight, a CBS News partner.

"I had a child with someone else and I had to tell [Union]. Hardest thing I've ever had to do is man up and tell Gabrielle Union that I've had a child with somebody else," Wade says in the documentary, according to ET. "I couldn't sleep. I wasn't eating."

"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*** somebody's life up, that you care about, that you love, if it don't hurt you, then you're not human," Wade says in the documentary, adding that he and Union "went through something that you never want to go through and we still came out of it."

Wade and Union were able to overcome the difficult situation, marrying in 2014 and welcoming a baby girl, Kaavia, via surrogate last year. 

Although the power couple officially got together in 2008, it seems Wade was crushing on the actress a lot longer. Wade's manager reveals in the documentary that the basketball star had posters of Union in college. 

In the documentary, Wade also says his kids, Zaire, Xavier and Zaya, always loved Union and he included them in his proposal to her. "She wasn't just marrying me, she was marrying all this baggage," he says. Wade was also the guardian of his nephew, Dahveon, who is now 18. 

"D. Wade: Life Unexpected," which will air on February 23, features home movies and never-before-seen moments, according to ET. The film was "10 years in the making," Wade said in a tweet.

At the documentary premiere, Wade spoke to ET's Nischelle Turner about the things he opens up about in the film, including his 12-year-old child Zaya, who recently came out as transgender.

"Well, we're not the only family that deals with all the things we've spoken about," Wade told Turner at the premiere last week. "We're not the only family that had to deal with surrogacy to bring our daughter [Kaavia] into the world. We're not the only family that's had to deal with gender expression, gender identity, sexuality, with their child," he added, referring to Zaya.

The 38-year-old added that his family understands God gave them a platform and, while it's not always a "popular thing" to speak out on issues people may be uncomfortable with, his family understand they are in a position to do so and they use their platform. 

On Tuesday, Wade opened up further about Zaya, telling "Good Morning America" that he and his family "love the fact that she doesn't have to hide who she is."

"She is our leader," he said. Zaya, who was named Zion at birth, knew she was transgender since the age of 3 and eventually started doing more research herself, Wade said.

"She was the one that sat down with us as a family and said, 'Hey I don't think I'm gay.' And she went down the list and said this is how I identify myself — I identify myself as a young lady. I think I'm a straight trans, because I like boys,'" Wade said on GMA. 

Wade also added he struggled with how much he wanted to talk about in the documentary, knowing it would be a big conversation. "This is no game to us. We're about protecting her heart and about protecting her joy and we have to support them," he said.