I've always been intrigued by this 'mystery' Diamond Tiara worn by Helen, Duchess of Northumberland, the Mistress of the Robes of the Queen Mother, which was notably worn for a Gala Performance at Covent Garden in 1950 and the Opening of the Royal Festival Hall in 1951, as well as an Gala Performance during the Belgian State Visit in 1963, which was just a few months before the Northumberland Strawberry Leaf Coronet was pulled out of her hands.

The design of the Northumberland Tiara is almost identical to the Diamond Tiara worn by Princess Dina of Hijaz when she married King Hussein of Jordan in 1955.