Credit: Mike Marsland/

While the fashion world waits with baited breath to find out which designer Kate Middleton will wear at her April 29 wedding to Prince William, the groom-to-be's suit for the big day is all set.

"He was measured long ago and had fittings at the Clarence House," a source close to William's Savile Row tailor Gieves & Hawkes confirms to "It's been finished by hand and is ready for the wedding."

PHOTOS: William and Kate's post-engagement engagements

And the future king's "I do" outfit is being kept under lock and key literally. The suit is stashed at a hidden location and when it's time to move it, a bullet-proof vehicle will be used, adds the source.

All the precautions might not be a terrible idea, adds the insider. "There's only one -- no spares!"

Recently Prince William's younger brother Prince Harry, opened up about the impending marriage, calling it "a big deal."

"My brother is very lucky," he told Good Morning America. "She's very lucky to find my brother. The two of them are a classic match."

For more on the Royal Wedding, including rare photos, interviews with family and friends, details on Kate's new life as a princess and a tour of their lavish homes, order a copy of Us Weekly's Will & Kate: The Royal Wedding now.