The Duchess of Sussex was dressed in a fitted black one shoulder gown, made by her wedding dress designer Clare Waight Keller.
The pregnant 37-year-old skipped the heels for Karat sandal in gold designed by Tamara Mellon.
Her unannounced appearance, where she was introduced onto the stage by British actress Rosamund Pike, saw her present the Givenchy creative with the award for womenswear designer of the year.
HELLO!'s Editor-in-chief, Rosie Nixon, was there to watch the spectacular moment and she revealed that Clare was "obviously stunned and surprised - she had no idea."
"It's so nice to see so many familiar faces," the 37-year-old said.
"I've had the pleasure meeting many of you. Thank you for the warm welcome. As all of you in this room know, we have a deep connection to what we wear."
"Sometimes it is deeply personal. Sometimes it is emotional."
"But for me this connection is driven in being able to understand it is about supporting and empowering each other especially as women."
Clare thanked Harry's wife for “trusting her” to design her gown for “the most important day in her life.
"This woman is so amazing. I got to know Meghan on such a personal level, and to have someone like that trust you in an incredible moment in their life is something that is just the most unbelievable honour and I can’t thank you enough."
The event took place at Royal Albert Hall on December 10, 2018 in London, England.
The stunning silk gown that Meghan, 37, wore for her May wedding to Prince Harry featured an open bateau neckline and sculpted waist. The train flowed in soft round folds cushioned by an underskirt in triple silk organza.
The process was “very collaborative,” Waight Keller said in an interview the day after the wedding, adding that Meghan was familiar with her work.
“It was a wonderful way to start the collaboration with her, finding out what she wanted for her day and just to find the absolute perfect style for her,” Waight Keller told reporters.
“Part of it was really a conversation in the beginning and then through a series of sketches that I proposed to her. We exchanged conversations about what would be the ultimate lines and proportions and the scale of the dress.”