That's the same church where "Suits" actress Meghan Markle married Prince Harry in May this year, and Eugenie was driven in the same auto that took Kate Middleton to her 2011 wedding to Prince William, which took place at Westminster Abbey: the 1977 Rolls Royce Phantom VI. "She has been through so much, and has come out a total victor!" he tweeted.
Tamara Beckwith, a friend of Eugenie's mother Sarah Ferguson, posted a sweet photo of her son enjoying a cupcake in a tent filled with lights, greenery and delicious snacks for attendees.
This isn't the first time Dougal has designed a garment for the royal though, as Eugenie wore one of his stunning creations to the wedding of Prince Harry and Meghan, Duchess of Sussex, in May this year.
The newlyweds are said to be "delighted" to share the four photographs which were taken by British fashion and portrait photographer Alex Bramall.
Model Kate Moss arrived with her daughter Lila Grace Moss Hack, whilst fellow models including Naomi Campbell, Cara and Poppy Delevingne, and Pixie Geldof were also in attendance at the event. "Readers have followed the exploits of Eugenie's parents Andrew and Fergie for decades, so I think they'll love sharing in this special occasion of their youngest daughter".
More than 800 guests attended the wedding, including pop star Robbie Williams and his wife, actress and TV presenter Ayda Field.
Princess Charlotte and Prince George made a memorable appearance on the Buckingham Palace balcony on the afternoon of last month's Trooping the Colour ceremony - part of the Queen's official birthday celebrations.
Posen added that he drew inspiration from "the beauty of Windsor and the surrounding countryside" where the wedding took place.
"Princess Eugenie is wearing diamond and emerald drop earrings which were a Wedding gift from the Groom".