Lady Sarah McCorquodale was seen sitting near King Charles . With just veteran Joy Trew, 98, between them, the two were seen engaging in conversation as fans spotted the unexpected reunion.

The interaction took place when they joined forces to put a blanket over Joy, with the pair seen laughing in the process. Lady Sarah, 70, - whom eventually married in 1981.

She is known to have joined the celebrations as a result of her prominent role in the Stamford branch of the Royal British Legion - which is a charity which provides social and emotional support to members and veterans of the Armed Forces.

Prior to the now-King dating her younger sister, Charles and Lady Sarah met at the annual Royal Ascot house party at Windsor in 1977.

Sarah then invited Charles for a shoot at their family estate, Althorp - which is where he met the then-16-year-old Diana.

In his and Diana's engagement interview, Charles said: "I remember thinking what a very jolly and amusing and attractive 16-year-old she was.

"I mean, great fun, and bouncy and full of life and everything."

Rumours of a proposal between Lady Sarah and Charles came to an end when their romance ended in 1979.

Although there is now no bad blood between the two, Lady Sarah gave a revealing interview to two journalists.

After Charles's engagement to Diana, Sarah revealed that she had set to two of them up. She, at the time, told : "I introduced them. I'm Cupid".