Esperanza Chávarri Aldecoa, Countess of Villagonzalo and wife of Fernando Maldonado Salabert, 8th Count of Villagonzalo, owned the tiara that dates to c.1900.
The countess was a lady-in-waiting of Victoria Eugenie of Battenberg, Queen Consort of King Alfonso XIII of Spain and the tiara has remained in the countess’ family for more than 110 years.
It is now being toured by Bonhams in Hong Kong, Geneva and New York ahead of its sale in London on September 26.
The tiara, which was exhibited at the National Museum of Decorative Arts in Madrid, is estimated at £80,000-120,000. It was designed as a double diadem that can be detached to form two separate tiaras, one of which is designed to be further converted to form a choker.
Johann Leibbrandt, senior valuer at Bonhams Spain, said: “This tiara has a lightness and lace-like quality made possible by working in platinum, a metal that is as light as it is strong. Jewellers only began to understand how truly to exploit platinum from around 1900, so it is particularly interesting that this tiara is noted in Ansorena's archives as being conceived as early as 1890.”