Wade had reportedly known the woman "for many years," a source told "Entertainment Tonight," which first reported the news.
Union, 41, of "Being Mary Jane," reportedly knew about the child before Wade proposed, the site said. And E! Online reported that the actress was angry when she first heard the baby news and distanced herself from her beau.
The pair, who have been dating since 2009, have worked through the issue privately as a couple, according to ET.
Now everything seems to be coming up just dandy for Dwyane.
Wade proposed to Union with an 8.5-carat ring ring last week. Union flashed her new sparkler when she attended the Heat's game against the Los Angeles Lakers at Staples Center on Christmas Day, and the couple even sent out Christmas cards together from the "Wade-Union Family."
The actress and ballplayer are still very much committed to spending their lives together, the ET source said, and are looking to get married in September.
Wade "takes the responsibility of being a father very seriously," a source told Gossip Cop about the third child.
The basketball star is currently raising his nephew Dahveon Morris and has full custody of his two sons -- Zaire Blessing Dwyane Wade and Zion Malachi Airamis Wade -- from his five-year marriage to high school girlfriend Siohvaughn Funches. The pair split in 2007 and their long-running divorce wasn't finalized until 2010, with the custody battle continuing into 2011. Since then, Wade authored the book "A Father First: How My Life Became Bigger Than Basketball," dedicated to the three boys, plus Wade's grandmother.
Union married football player Chris Howard in 2001, but they separated in 2005 and divorced in 2006.
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