A rare turquoise and diamond Cartier tiara once owned by Viscountess Nancy Astor is set to headline Bonhams’ London Jewels auction on June 5. The tiara, which has remained out of the public eye since it was acquired by Lord Astor in 1930, is estimated to fetch up to £350,000 ($461,864).

Crafted by Cartier, the tiara features a central old brilliant-cut diamond surrounded by a mix of old brilliant-, single-, and rose-cut diamonds. Three turquoise plumes accented with diamond stems rise from the center, while each side is adorned with a fan-shaped turquoise panel design.

Viscountess Astor, born Nancy Witcher Langhorne, was a trailblazing American-born British politician and the first woman to take a seat in the UK Parliament, serving from 1919 to 1945. She met her husband, Waldorf Astor, during her transatlantic journey to England in 1905.

The auction will also showcase several other standout pieces. A toi et moi ring featuring a 2.05-carat fancy-pink diamond paired with a 1.42-carat fancy-bluish-green diamond is valued at up to £250,000 ($329,971). A trio of mid-19th-century antique rose-cut diamond brooches could achieve £80,000 ($105,593), while a Tiffany & Co. pavé-set diamond and gem-set leaves necklace is estimated at £60,000 ($79,193).

Also on offer is a pair of diamond chandelier earrings, with cascading pear-cut diamonds weighing 3.17 and 4.02 carats, expected to bring in up to £60,000. Rounding out the highlights is a 1930s Cartier clip brooch with circular-cut citrines and old brilliant-cut diamonds, estimated at £20,000 ($26,398).