Sophie, Duchess of Edinburgh, 58, was invited to an investiture for a promotion in her role with the Order of St John on Thursday.
The late Queen Elizabeth II bestowed the honour to become a Dame Grand Cross last year.
Sophie is currently the Grand President of the St John Ambulance and does a lot of work with the organisation.
On Thursday, she was invested as a Dame Grand Cross by the Duke of Gloucester, the Grand Prior of the organisation.
For this occasion, the Duchess wore a gorgeous Suzannah London “Evangeline” dress in black, which she previously wore to Prince Philip’s funeral.
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Sophie also wore this dress for the late Queen’s funeral procession in Edinburgh in September 2022.
Royal fashion finder @dagmar_Marie77 offered a reason why the Duchess may have chosen this dress for her investiture.
She tweeted: “She rewore her bespoke Suzannah Evangeline dress that she previously wore for both Prince Philip’s funeral and for Her Majesty Queen Elizabeth II’s funeral procession in Edinburgh.
“No doubt she was keeping them close today as Queen Elizabeth II was the one who appointed her just last year.”
The description for this dress says: “The Evangeline is a modern interpretation of a retro archive piece.
“Made in a black mid-weight Italian crepe, contrasted with an exquisite swoosh of black silk.
“Fastened with a centre back invisible zip for step-in ease and small buttons at the back neck.
“The slim sleeves and high neckline add a beautiful dynamic to this wonderfully elegant fit and flare midi length dress, perfect for weddings, racing and red carpet.”
In addition, Sophie wore her Christian Dior Mise en Dior Pearl Hoop Earrings which she has owned since 2015.
These Christian Dior pearl “huggie” hoop earrings are from the Cruise 2015 collection, and look elegant on the Duchess.
Sophie wore her blonde hair in a low bun for the occasion and donned a pair of black stiletto heels.
Royal fan @Mari_Edinburghs tweeted about her dress: “It was really a meaningful choice.” Similarly, @GertTheGreatest wrote: “She looked like a goddess.”