Lady Sarah Chatto was among those who showed her support to Queen Camilla at the Queen's Reading Room Literary Festival on Saturday.
The cousin of King Charles and her husband Daniel Chatto joined the reception by authors, actors and supporters of literature including Helena Bonham Carter, Harlan Coben, Miriam Margolyes, Lee Child and Ian Rankin.
Queen Camilla, 76, was seen warmly embracing Lady Sarah, 60, at the event which took place at Hampton Court Palace in Surrey.
Lady Sarah, who is an artist and painter, looked lovely in a periwinkle dress and coordinating cardigan while accessorising with espadrille wedges and a black crossbody.
The daughter of the late Princess Margaret and her brother, David, 2nd Earl of Snowdon, have always shared a close relationship with their cousins, King Charles and Princess Anne.
Lady Sarah often joins the royals at major events, including King Charles' coronation, the annual Easter Sunday service in Windsor and Royal Ascot.
At the event, Queen Camilla took the time to greet guests before watching a short excerpt from A Midsummer Night's Dream performed by Downton Abbey star Elizabeth McGovern.
The actress met Camilla afterwards, and then said during their conversation she was "expressing my support and gratitude for the work she's doing with this charity".
The Queen then joined the audience of thousands of people at the festival's evening session in Base Court, which included a performance by Harry Potter star Miriam and highlights from her one-woman show.
This is the second year that the festival has taken place, with both the King and Queen attending last year. The former Duchess of Cornwall launched The Reading Room on Instagram in January 2021 and the project was relaunched as charity The Queen’s Reading Room in February 2023.
It also has a podcast whose second series guests included Good Omens and Stardust author Neil Gaiman and Withnail And I actor Richard E Grant.
The Queen's Reading Room festival is a co-production between The Queen's Reading Room and Historic Royal Palaces, the independent charity that cares for Hampton Court Palace.