Credit: Mario Testino/Art Partner

Say cheese!

Clad in matching white shirts, Prince William and bride-to-be Kate Middleton beam for the camera in a beautiful, black-and-white portrait; Us Weekly is the very first U.S. website to sneak a peek at the the unforgettable shot on the eve of their historic April 29 wedding.

Taken by famed photographer Mario Testino -- the man behind the couple's memorable engagement photo as well as iconic shots of the late Princess Diana and countless celebs -- the lovely new pic appears in the Royal Wedding program, which became available for download on Thursday.

When Testino photographed the couple for their engagement portrait (released in early December), he was floored by the honor.

"I am very happy to have been asked to cover this historic moment that the whole world was waiting for. They are in their prime and brimming with happiness," Testino said. "I have never felt so much joy as when I see them together."