Lady Helen Taylor was joined by her closest family and friends at her 60th birthday celebrations last weekend.
The Duke of Kent's daughter was presented with a cake, complete with sparklers, by children, Eloise and Cassius.
Lady Helen's niece, Lady Marina Windsor, shared a glimpse into the glamorous soiree on her Instagram account, according to Tatler.
The gathering took place inside a large marquee, complete with a long dining table for guests, which was decorated with flowers, foliage and tealights.
Lady Helen shares four children with her husband and art dealer, Timothy Taylor – Columbus, 29, Cassius, 27, Eloise, 21, and Estella, 19. They are all behind their mother in the line of succession, who is 47th.
Cassius, who studied art management at Goldsmiths University, runs his own events company, Telltale and loves to DJ in his spare time, while Columbus works as an Associate Director at his father's international gallery.
Lady Helen's children are close to their cousins, Lady Marina, Lady Amelia and Edward Windsor, who are the children of George Windsor, Earl of St Andrews and Sylvana Tomaselli.
George and Lady Helen also have a younger brother, Lord Nicholas Windsor, who forfeited his right of succession to the throne after his conversion to Catholicism in 2001.
It's not known whether Lady Helen's parents, the Duke of Kent, 88, and Katharine, Duchess of Kent, 91, were present at the party.
The Duke of Kent is a first cousin of the late Queen Elizabeth II, who still carries out official royal engagements.
Earlier in April, he visited the recently redeveloped Blackheath Halls in South London and took part in his last parade as Colonel of the Scots Guards before handing over the role after 50 years to the Duke of Edinburgh.
Lady Helen, who was born on 28 April 1964 in Iver, Buckinghamshire, isn't the only member of the British royal family to mark her 60th birthday this year.
Princess Alexandra's son, James Ogilvy, and Prince Edward celebrate the milestone in February and March respectively, while the late Princess Margaret's daughter, Lady Sarah Chatto, turns 60 on 1 May.
The foursome were pictured together for a portrait at Windsor Castle to mark their 21st birthdays in 1985.
Lady Helen, who is a former muse for Giorgio Armani, looked fashion-forward in a blue satin dress and pearls, while Lady Sarah wowed in a pink off-the-shoulder gown for the photograph.
Having previously worked with art dealer, Karsten Schubert between 1987 and 1991, Lady Helen is a patron of the CLIC Sargent children's cancer charity and a trustee of The Royal Marsden Cancer Charity. She is also on the advisory board of the Glyndebourne Festival Opera.