Crystal Renay -- who married Ne-Yo in February 2016 -- filed divorce docs earlier this week in Atlanta saying the couple's marriage is "irretrievably broken with no hope for reconciliation."

What's most shocking, Smith says that while she and Ne-Yo have three children together of their own -- he recently fathered a child with another woman. Crystal lists the couple's date of separation as July 22, 2022 ... and says she's been taking care of the three kids since the split.

Crystal is asking for primary physical custody of the kids and joint legal custody -- she's also asking for child support and alimony.

Ne-Yo and Crystal have had their ups and downs over the years, she filed for divorce back in 2020 but later withdrew her petition. TMZ broke the story, the two celebrated their love once again in 2022 in Vegas with a "second" wedding.