Photos show Beatrice, 33, wearing a sleek brown satin skirt with Eugenie, 31, dressed stylish in all black. The dinner was to launch Ms Blunt's Loci vegan sneakers. It was held in aid of the Blue Marine Foundation, a charity dedicated to protecting the world’s oceans - of which Princess Eugenie is an ambassador.

       Princess Eugenie, 31, gave birth to her son, August, in February 2021.

       She married her husband, Jack Brooksbank, in 2018. Mr Brooksbank did not attend the intimate charity event.

       Older sister Beatrice, 33, welcomed baby Sienna Elizabeth with husband Edoardo Mapelli Mozzi in mid-September.

       Sharing their baby’s name on Twitter in October, Beatrice wrote: “We are delighted to share that we have named our daughter Sienna Elizabeth Mapelli Mozzi.

       “We are all doing well and Wolfie is the best big brother to Sienna.”

       Wolfie, Beatrice’s step-son, is Edoardo’s son from a previous relationship.

       Wednesday's dinner was Beatrice’s first outing since Sienna’s birth. The princess was joined by Edoardo, 38, as they posed with James and Sofia Blunt.

       The royal sisters were also spotted together last month, decked out for the wedding of Prince Philippos of Greece and Denmark.

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       He married Princess Nina in a lavish ceremony after a lockdown civil ceremony attended by just their fathers.

       Eugenie also attended the COP26 climate change conference in Glasgow, alongside Princes Charles, Prince William, Kate Middleton and Camilla.

       On her Instagram account, Eugenie described her visit to COP26 as a “wonderful first day at COP26 meeting and speaking to some of the most inspiring initiatives and people out there.”

       Eugenie often shares her pride for older sister Beatrice on Instagram.

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       After two-month-old Sienna was born, Eugenie posted an emotional tribute to her “dearest Beabea and Edo？.”

       She said: “Congratulations on your new angel.

       “I can't wait to meet her and I'm so proud of you.

       “We're going to have so much fun watching our children grow up.”

       She signed off with: “Love Euge.”

       She then addressed a quick note to her “new niece”, writing: “I love you already and think you're just awesome from the photos.. we're going to have so much fun ？together.”

       Beatrice and Edoardo have made their home at St James’ Palace in London, while Eugenie, Jack,and baby August reside at Frogmore Cottage, 21 miles away.

       Frogmore is the former home of Prince Harry and Meghan Markle in Windsor.