Credit: Michael Caulfield/

Hugh Hefner, 84, is one step closer to tying the knot with his 24-year-old bride, Crystal Harris.

The twosome will wed at the Playboy Mansion June 18, a Playboy rep confirms to

"It will be intimate with a close number of friends here at the mansion," Hefner has said of the nuptials. "No big blowout affair. Something very personal."

An insider tells Us they've set the list at less than 300 guests and that Harris is close to making one other important choice: the gown.

The insider says the Playmate -- who nabbed a $90,000 ring from her fiance -- is eyeing a strapless dress by designer Romona Keveza.