Now that fashion is moving away from cheap fixes towards enduring classics, wouldn't a 38-carat diamond pendant necklace , with an impeccable pedigree, make the perfect investment buy? Valued at £2.3m, it's part of a collection of gems once owned by Christina Onassis, late daughter of shipping magnate Aristotle Onassis. Forty pieces from her jewellery box will be the highlight of a 230-lot auction at Christie's in London tomorrow.

The company's European head of jewellery, Raymond Sancroft-Baker, believes that it's not just the timeless design of Christina's necklace that could attract bids pushing £3m, but the fact that the main diamond is a "major stone", a flawless, D colour diamond – the highest category. The identity of its famous previous owner is a selling point, too, despite her tragic story: Christina died in 1988 at the age of 37, having been through four divorces, frosty relations with her stepmother Jackie Onassis, and drug problems. In her early twenties, Christina had lost her brother in a plane crash, her mother committed suicide, and her father died of pneumonia. Christina's daughter Athina, who was only three years old when her mother died, is selling the pieces because they don't fit in with her lifestyle.

Sancroft-Baker says the value of such high quality diamonds has doubled in the past two years, with a small group of international super-rich on the lookout for tangible investments.

There are cheerful stories behind some of Christina's pieces. A Fabergé Buddha made of bowenite used to sit inside the study of Aristotle Onassis's yacht, named after his daughter. The motion of the boat would make the hands, ruby tongue and head bob about, and when guests boarded the vessel, Onassis would introduce them to the waving figure – a billionaire's toy, now yours for the high estimate of £350,000.