A diamond single-stone ring, mounted by Cartier. photo Bonhams

The marquise-cut diamond, weighing 6.01 carats, within a platinum mount, signed Mtd Cartier London, maker's mark, numbered, London hallmark, ring size I½. Estimate: £45,000 - 50,000, US$ 72,000 - 80,000I

Bonhams.Fine Jewellery, 25 Apr 2012. London, New Bond Street www.bonhams.com