Princess Elizabeth as she was then, got engaged to Prince Philip of Greece just after WW2 ended. He was cash-strapped, so the ring was made from the diamonds taken from an old tiara that belonged to his mother Princess Alice of Greece (thank goodness for old family heirlooms!)
It was a platinum ring, with a 3 carat diamond in the centre flanked by eight diamonds, four on each side.
The size of the jewels are modest compared to Princess Diana's/Kate Middleton's ring, but I think they suited Elizabeth. The young Elizabeth was demure and understated and the modest unflashy ring reflected that and reflected the austerity of the late 1940's..
