Credit: Mario Testino/Clarence House Press Office

Here's something to help remember one of the most unforgettable weddings ever: To commemorate Prince William and Kate Middleton's impending nuptials, a souvenir official program will be published and sold, with the cover released on Tuesday.

Continuing a royal tradition, the program will feature a full Order of Service, a personal thank-you message from Middleton, 29, and William, 28, plus a never-before-seen photo of the couple taken by photographer Mario Testino (who snapped their famous engagement portrait).

The cover image features Prince William's Coat of Arms -- with the Middleton family's just-released Coat of Arms on the back.

The program will be sold (by royal army cadets and scouts) along the wedding route and surrounding areas on April 29; proceeds will benefit the Foundation of Prince William and Prince Harry, which aims to help vulnerable children, fund sustainable development locally and ensure the welfare of veterans and their families.

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.