Hefner's Revenge -- I'm Altering Crystal's Cover

Hugh Hefner is finally taking action in his unexpected break-up with Crystal Harris -- defacing her Playboy cover with a giant red sticker that reads, "Runaway Bride."

Before Crystal called off the wedding ... just days before their wedding ... Hefner had already agreed to give her the July cover with the headline, "Mrs. Crystal Hefner."

Box loads of magazines have already been shipped without the sticker -- but Hefner insists the big, red mark WILL appear on newsstands.