Jane Seymour -- Legally Separates from James Keach

Jane Seymour, aka TV's Dr. Quinn, has officially pulled the plug on her marriage to actor/director James Keach, filing for legal separation ... TMZ has learned.

Seymour filed the docs late last week in L.A. County Superior Court ... citing irreconcilable differences.

62-year-old Jane and 65-year-old James have been married for more than 20-years and have 17-year-old twin boys. In the papers, Jane requests joint legal and physical custody.

The couple announced in April that they were splitting up, and negotiating terms of a divorce ... but the docs make the split official.

The former Bond girl is not requesting spousal support.