The iconic fashion designer tells ET that she was 'proud' and honored' to be a part of Markle's 'royal day.'
After the pomp and splendor of Markle's dream wedding to Prince Harry on Saturday at St. George's Chapel in Windsor Castle -- followed by a luncheon hosted by Queen Elizabeth at St. George's Hall -- the 36-year-old bride changed out of her elegant Givenchy wedding gown and into a stunning McCartney dress for the private evening reception.
"I’m so proud and honored to have been chosen by the Duchess of Sussex to make her evening gown and represent British design," McCartney told ET on Saturday.
The elegant, hip-hugging lily white dress -- made of silk crepe --featured a high neck and exposed shoulders, as well as an open back.
McCartney added that getting the opportunity to design the incredible ensemble has "truly been one of the most humbling moments of my career and I am so proud of all the team on this stunning royal day."
Markle looked radiant as she left Windsor Castle alongside her tuxedo-clad new husband. The pair hopped in a silver blue Jaguar E-Type Concept Zero, en route to the reception at Frogmore House.
Complementing the McCartney dress was the massive aquamarine ring Markle wore on her right hand. The stunning, emerald-cut sparkler was a gift from Prince Harry, and once belonged to his late mother, Princess Diana.
This evening's reception will have the bride and groom's close family and friends in attendance, and will include a speech from Meghan. This will be the first time she's spoken publicly as the Duchess of Sussex. The title of Duke and Duchess of Sussex was officially bestowed upon the couple by the Queen just before they tied the knot.
For more on Markle's elegant wedding gown -- designed by Clare Waight Keller, the artistic director of Givenchy -- and how it paid tribute to the late Princess Diana, check out the video below.
Prince Harry Gifts Princess Diana's Stunning Aquamarine Ring to Meghan Markle on Royal Wedding Day
Meghan Markle and Princess Diana: How Prince Harry's Fiancée Measures Up to His Late Mother (Exclusive)