The couple became engaged on New Year's Eve when Crane proposed as they were on a beach in the Maldives.
"From about three years into our relationship, I think we both knew we would get married one day," Harding told Hello magazine. "But when the moment came, I wasn't expecting it at all. And although Tom stumbled over his words a little, I loved that because it was really sweet and heartfelt. He hadn't rehearsed a big speech - he was saying how he really felt."
Crane revealed that he decided to propose after seeing a ring he thought was perfect for the Girls Aloud star.
"I knew Sarah wanted a central sapphire with diamonds," the DJ said. "There we were, about to see in a New Year in the most romantic place I've ever visited, and we spot this beautiful ring. I figured it had to be fate.
"The New Year's celebrations were gearing up and Sarah was chattering away, so much so that I had to say to her in the end, 'Will you just be quiet for a second and listen to me?' I pulled the ring out of my pocket, which I was amazed she hadn't spotted because it was in a big old box - got on one knee and asked her to marry me."
However, Harding admitted that she had taken the ring to be "blinged up" because she did not think it was "unique" enough.
"Kind of a 'pimp my ring!'" she quipped, adding: "I absolutely love it."
> Harding: 'Wedding planning is stressful'