Designer Vivienne Westwood, 70, who is a close friend of Moss for 15 years, let the secret slip last week, reports dailymail.co.uk.
Asked if she had been approached to create the wedding dress, Vivienne said: "No, I think she's designing it herself. She has done her own fashion range and she knows about clothes. She knows what she is doing, she doesn't need my help."
"Kate is a mate. I've known her for years and I'm really happy for her," she added.
Moss earlier sold her own fashion range through High Street chain Topshop. She and Hince have been together for three-and-a-half year, but became engaged only this month.
