Hugh Hefner will get married on June 18.
Speaking to TV talk show host Piers Morgan, Crystal said: "The date of the wedding. Can I tell him? It is June 18th. This year, Saturday. We're excited. "
Hugh added: "A June bride. It will be at the Mansion but it will be a little more intimate."
Hugh's second wedding to Kimberley Conrad - the mother of his sons Marston, 20, and 19-year-old Cooper - also took place at the Playboy Mansion, but he and Crystal plan to make sure their nuptials are not an exact replica.
Crystal explained: "It's going to be fun. I mean he got married once in The Front yard so I asked if we could do it in the backyard."
The 84-year-old media mogul also revealed he and Crystal, 24, have decided who will be part of their wedding party.
He explained: "My brother will be my best man. The groomsmen will be my two youngest sons, Marston and Cooper."
Crystal added: "The bridesmaids are my best friend, Ana, as my maid of honour, and my two sisters are going to be my bridesmaids."
Hugh - who also has children Christie, 48, and David, 45, from his marriage to first wife Mildred Williams - and Crystal have been dating for around two-and-a-half years.