The Greek prince wed Nina Flohr, the daughter of a billionaire, in Athens this weekend, with representatives from almost every monarchy in Europe likely to have attended the wedding.
Eugenie and husband Jack Brooksbank invited the newlyweds to their own royal wedding in October 2018, while Beatrice's husband Edoardo Mapelli Mozzi is good friends with the bride.
Beatrice wore a long-sleeved maxi dress from Gucci that included a plunging neckline studded with jewels and a long black skirt with a sequin bow. Edoardo kept things simple in a black suit.
The Princess recently welcomed daughter Sienna Elizabeth Mapelli Mozzi on 18 September.
Eugenie, meanwhile, wore a long black gown by Peter Pilotto with a thigh-high split, while Jack donned a navy suit.
Prince Philippos' family is very closely linked to the British royal family – not only was Princess Diana his godmother but he was named after Prince Philip, one of his godfathers.
Philippos was born in London in 1986 at St Mary's Hospital and was raised in a house that bordered Hampstead Heath with four older siblings Princess Alexia, Crown Prince Pavlos, Prince Nikolaos and Princess Theodora.
Diana and sons Prince William and Prince Harry were frequent visitors.
Prince Philippos' parents Queen Anne-Marie of Denmark and King Constantine of Greece, who is Prince William's godfather, were in attendance along with numerous international royals.
The ceremony was the couple's third wedding after having two previous weddings, which were smaller and more intimate than this week's.
The pair's first wedding was last December in St Moritz, Switzerland, while their second was held at Vogue writer Alice Naylor-Leyland and her husband Tom's home in Cambridge.
Flohr, whose new title is Princess Nina of Greece and Denmark, wore "a white silk moire taffeta gown, modified from Chanel’s 2021 Autumn Winter Couture Collection" according to the royal fan site RoyalHats.net.
The website added she "topped her gown with a lengthy silk tulle veil and the antique corsage pearl and diamond floral tiara, a diadem of Scandinavian royal origin that Queen Anne-Marie inherited weeks before her marriage to King Constantine".
Princess Nina's father founded the luxury airline company VistaJet in 2004, while her mother Katharina Konečný, is a founding editor at Russian Vogue and a creative director at Fabergé.
Nina has previously worked for her father and later opened a luxury spa/ecological sanctuary on Benguerra Island off the coast of Mozambique.
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