Sources at Playboy tell us Crystal walked down the aisle around 7PM in front of an intimate group of family and friends -- a much smaller gathering than was originally planned for their June 2011 wedding.
That was canceled when ex-Playmate Crystal left Hef at the altar ... pulling the plug on their relationship days before the wedding.
We're told Crystal moved back into the mansion earlier this year, sorted out all the problems with Hef -- and then they decided to try the whole marriage thing again.
This is 86-year-old Hef's third wedding, and 26-year-old Crystal's first attempt.
If nothing else ... their reception should be kick ass -- it's the annual NYE bash at the mansion.