Hugh Hefner Set Wife Up with Millions Long Before Death

As quickly as Hugh Hefner said "I Do," he rolled out a plan to make sure his wife would be provided for when he dies ... a plan that included a sick pad and MILLIONS.

TMZ obtained the deed to a Hollywood Hills home that is held in trust ... a trust controlled by Crystal Harris. Hef bought the 5,900 square foot house for her back in 2013.

And get this ... sources familiar with Hef's estate plan tell us he also left Crystal $5 million. Based on what we know, the deal is part of a prenup Hef and Crystal signed before they got hitched in 2012.

As for the house ... it's got 4 bedrooms, 5 baths and an infinity pool.

Hef died peacefully in his L.A. home Wednesday. He was 91.