Shannen Doherty's ex-husband, Ashley Hamilton, is recovering in a hospital after suffering an apparent overdose ... TMZ has learned.

Sources with direct knowledge tell us the "Iron Man 3" actor was found last Thursday in an L.A.-area Airbnb, and was experiencing a medical emergency related to an unknown substance. We're told he was rushed to the hospital where he remains in stable condition.

Hamilton, who has appeared in a number of films over the years, famously married Doherty in 1993 after just 2 weeks of dating -- he was 19 at the time -- but the marriage lasted only five months before ending in divorce.

Beyond his acting career, 51-year-old Ashley comes from a well-known Hollywood family. He is the son of actor George Hamilton and Alana Stewart, and was once the stepson of rock icon Rod Stewart. He and his siblings -- including Kimberly Stewart and Sean Stewart -- starred in the short-lived 2015 reality show "Stewarts & Hamiltons."

Ashley has publicly battled addiction in the past -- reportedly going to rehab more than 30 times -- and has even become a sober companion to others coping with substance abuse.

We've reached out to family reps multiple times, but have not gotten a response.