“The sapphire is of a deep blue colour intensity, with two side stones that look to be around 0.5 carats each.

“It’s a very elegant, vintage design that sits beautifully on the finger.

“Because of the size of the stones, I would say this engagement ring would cost around £20,000 to create.”

Princess Anne’s first wedding, to Mark Phillips, a lieutenant in the 1st Queen’s Dragoon Guards, took place in 1973.