Heirloom piece from O’Briens of Dromoland a rare offering

A diamond tiara owned by the late Doreen O'Brien, a daughter of the 14th Baron Inchiquin, is likely to attract considerable interest at Sheppard's auction in Durrow on Tuesday. The classic heirloom piece – gold decorated with "in excess of 14 carat of diamonds" in its original leather case, from Hancocks and Co, Vigo Street, London – is believed to date from the 1930s and has an estimate of €6,000-€9,000.

The Hon Doreen O'Brien was a member of the aristocratic Irish family that had its seat at Dromoland Castle near Newmarket-on-Fergus, Co Clare. Her father was Edward Donough O'Brien, Lord Lieutenant of Co Clare and 14th Baron Inchiquin. Her mother was Ellen Harriet, daughter of the 2nd Baron Annaly; her sister Beatrice married the radio pioneer Marconi.

Doreen was born in 1888. In 1907 she married Richard Coke, a son of the 2nd Earl of Leicester who later became a major in the Scots Guards, fought in the first World War and, in 1957, established the record for the most grouse brought down by a single gun. They lived in Norfolk, England and had five children but divorced in 1927. She died, aged 72, in 1960.

The 16th Baron Inchiquin sold Dromoland Castle in 1962 to an American businessman and it later became a luxury hotel. According to the hotel’s website, “the pedigree of the Dromoland O’Briens is kept in a vault at Lloyds in London and is 36 feet in length”. Conor O’Brien, the 18th baron, and his family live in Thomond House and continue to farm and run part of the estate as a sporting and leisure estate.

Hancocks of London

The tiara has been consigned to auction by a family descendant. Sheppard's said it was very rare for a tiara owned by an Irish noble family to appear at auction. The fitted case bears the logo of Hancocks – a famous London jewellers – which today is located in London's Burlington Arcade. The company was founded in 1849, quickly received a royal warrant from Queen Victoria and was contracted to make the medals for the Victoria Cross, Britain's highest military award, which it continues to make exclusively. Hancocks also received a royal warrant from George V (who died in 1936) and later Queen Elizabeth, the Queen Mother (who died in 2002).

Hancocks' most famous commission was the so-called "Devonshire Parure" – a famous suite of jewels assembled in 1856 for the coronation of Tsar Alexander II of Russia. It was commissioned by the 6th Duke of Devonshire for Countess Granville, the wife of his nephew, to wear in Moscow at the coronation and consists of seven pieces of jewellery (including a bracelet, bandeau, comb, coronet, stomacher, necklace and diadem), all of which are set with a major part of the 2nd Duke of Devonshire's collection of gems.

The tiara – and other items from the collection of Doreen O’Brien – is on view from today along with hundreds of other items at Sheppard’s saleroom in Durrow, Co Laois where the auction, titled “Dublin & Provincial”, takes place on Tuesday.