Crystal Harris designed her own engagement ring.

The 24-year-old beauty admits she was not surprised when Playboy mogul Hugh Hefner, 84, proposed to her on Christmas Eve (24.12.10) because the couple had already discussed marriage, and she had chosen the stunning three-carat diamond-and-platinum band herself, with the assistance of her partner's secretary Mary O'Connor.

Crystal revealed: "I picked out the diamond with Mary. It all happened so fast and we're happy. Nothing's changed. Everything is the same."

As to how Hugh - who has been married twice before - proposed, the Playmate explained he wound up a 'Little Mermaid' music box and asked her to open it, revealing The Ring inside.

He then said: "I hope it fits."

The couple are hoping for a summer wedding with "close friends and family" at the Playboy Mansion, and Crystal says her parents have given the nuptials their blessing.

She said in an interview with E! online: "Both my parents are super supportive of everything and whatever makes Hef and I happy makes them happy. I couldn't be happier."

However, the pair do not plan to start a family of their own as Crystal is content to focus on her aspiring music career.

She said: "I just have a bunch of different projects I'm working on and that's fun for me so that's what I'm going to do."

Because she is branching out in her career, the blonde beauty has no qualms about signing a prenuptial agreement if she is asked to.

She said: "Whatever Hef wants me to do. I'm happy. I have the singing thing going for me and other things so whatever he wants. I don't know anything about that stuff. I don't care. Whatever."