Middleton sported an elegant, cropped fitted black jacket over an above-the-knee ivory dress to attend the Thursford Christmas Spectacular in Norfolk, England, on Dec. 18.
The event benefits the Teenage Cancer Trust, and the striking couple planned to meet with some of the charity's benefactors during an intermission, the Daily Mail reports.
The princess-to-be's dress was noteworthy for its beautiful detail work, which included fabric cutouts along the neckline, accented by beading and small crystals. A slim black cummerbund, along with the jacket's flattering cut, accented Middleton's waist. The dress' skirt appeared to have two or three layers of fabric, which gave it fullness as the future princess walked in her black pumps.
The royal fiancée carried a sleek coordinating clutch and flashed her heirloom Princess Diana diamond-and-sapphire engagement ring and a broad smile as the crowd cheered the couple's arrival.
Prince William wore a classic, well-cut navy suit, red patterned tie and striped shirt most likely by Turnbull and Asser, the official royal shirtmakers ..
Middleton's creamy frock was similar in hue to the Reiss dress and Whistles blouse she wore for her official Mario Testino engagement photos.
When she stepped out solo for a charity concert in London a few weeks ago, it was in a black overcoat and matching suede boots.
Middleton, who also lunched at Buckingham Palace with Queen Elizabeth II on Dec. 17, appears to be embarking on her official roll-out as a member of the royal clan.
"Between now and the wedding there will be occasions when Catherine does shadow Prince William to learn the ropes and see how things go," a palace official told People.
The prince had a festive fashion comment for some teenage well-wishers in the crowd. "Cool hats," he reportedly said to a group wearing elf toppers.
Meanwhile, read about the sheer dress Middleton wore when she met her prince. It's now considered a valuable royal artifact.
Also, find out the crazy things designers are doing for the chance to design Kate's wedding dress.
And read the latest installment in our "Great Royal Weddings" series about the marriage of Britain's Princess Anne to Lt. Mark Phillips.