Her blue velvet dress with a white floral pattern featured a mock turtleneck, long flared sleeves and a flounced hem.
Prince William complemented his wife's dress in an electric blue suit for the evening event at the Fotografiska Gallery, which boasts glittering views over Stockholm and to which they traveled by boat.
It was the first time the baby was seen in public since his April 23 birth, and the first time the Cambridge family of five, including Prince William, Prince George and Princess Charlotte, were seen together in public since the birth.
It's hard to see Duchess Kate's dress thanks to the baby's christening gown Archbishop of Canterbury Justin Welby's vestments, but she's wearing a creamy Alexander Mc Queen dress with a V neck and puff sleeves, plus a headband-style hat by Jane Taylor.
Duchess Kate of Cambridge enjoyed an afternoon of play with her children, Prince George and Princess Charlotte (doing a somersault), while Prince William played in the Maserati Royal Charity Polo match on June 10, 2018 in Gloucester, England.
A day before the Cambridge family outing at the polo match, they were on royal duty for the Trooping the Colour parade celebrating the queen's official birthday on June 9, 2018.
Princess Charlotte and her mother, Duchess Kate of Cambridge, after the wedding of Prince Harry and the former Meghan Markle on May 19, 2018.
She wore a cream Alexander Mc Queen coat dress with a pale yellow hat.
Duchess Kate and Prince William met with academics and practitioners to discuss Sweden's approach to managing mental health challenges during day two of their visit to Sweden, Jan. Under her red-checked Catherine Walker coat, she wore a cream Alexander Mc Queen dress that showed off her baby bump.Check out Duchess Kate's Goat coat when she opened an Action on Addiction treatment center in Essex: The coat, in a striking marine blue that stood out among the men's dark suits, also showed off her still-slight baby bump.Kate, 36, is due to give birth in April to her third child.Kate, who shared a carriage with her stepmother-in-law, Duchess Camilla of Cornwall, wore a pale blue Alexander Mc Queen dress with a floral-detailed hat by Juliette Botterill.The two royal sisters-in-law, Duchess Kate and Duchess Meghan, on the balcony of Buckingham Palace during the Trooping the Colour parade celebrating the Queen's official 92th birthday on June 9, 2018. The two wore similar saucer-shaped fascinator hats.Duchess Kate of Cambridge wore an Alexander Mc Queen coat dress with a matching hat by Sean Barrett, plus a diamond and ruby Darce brooch from the Air Cadets, for the day of celebrations marking the RAF centenary on July 10, 2018, in London.