Brittney Griner has filed for divorce from her wife, Cherelle -- the woman who stood by her when she was locked up in Russia -- after eight years of marriage.

The WNBA star filed the divorce petition Thursday ... and lists July 24 as the date of separation. She says their marriage is "irretrievably broken."

Brittney and Cherelle -- who share one child together -- tied the knot back in June of 2018 ... and remained together during the 10 months Brittney spent in a Russian prison.

Brittney's asking the court for joint legal custody and to determine how much child support to award, if any at all.

While Brittney balls up the basketball court, Cherelle dominates the court of law ... she's an attorney and was a leading advocate in pushing for Brittney's release from Russia back in late 2022, months after she was sentenced to 9 years in a Russian prison for allegedly possessing marijuana.

Cherelle told People that she felt "hopeless" during Brittney's prison sentence ... and she told them all about their tearful reunion.

Griner -- a 9-time WNBA all-star -- is averaging a team-high 14.1 points per game with the Connecticut Sun this season.