Kenny G Files for Divorce

Kenny G has filed for divorce from his wife, TMZ has learned -- this after his wife filed for legal separation back in January.

In the court docs -- filed Thursday in L.A. by Kenny's disso-queen attorney Laura Wasser -- the musician cites "irreconcilable differences" as the reason for the split from his wife Lyndie Benson-Gorelick. They've been married for 20 years.

In the docs, Kenny indicates there IS a prenup -- which is significant because Kenny's worth a reported $50 million.

Kenny also asks the court for joint legal and physical custody of the couple's minor son.

TMZ broke the story ... Lyndie filed for legal separation in January, also citing "irreconcilable differences." We're guessing Kenny just got sick of waiting for her to file for divorce, so he made the first move.