Three-time divorcee Charlie Sheen is hopping back on the marriage wagon ... this time to former adult star Brett Rossi.
Sheen proposed Saturday morning after he flew Rossi to Hawaii on a private jet -- then bragged about the proposal to a local photog who snapped some pics.
Sources close to Sheen confirmed the engagement is for real to TMZ ... but so far, no additional details.
Sheen was first married in '95 to model Donna Peele but the couple split up a year later. In 2002, Sheen tied the knot with Denise Richards ... but she surprisingly filed for divorce two years later while six months pregnant with their second kid.
Brooke Mueller got the lucky title of wife #3 in 2008 ... but they were divorced in 2011 after a tumultuous relationship -- including an incident where she accused Sheen of holding a knife to her throat on Christmas morning.
For what it's worth ... sources close to Sheen tell us they're confident this relationship is different than the others -- and he's taking things incredibly serious this time.
Hopefully Rossi doesn't get Kelly Preston'ed.