Guy Wildenstein poses in front of never before seen Monet painting “Villas at Bordighera, 1884”

They are among the most powerful people in the art world, with an empire said to include masterpieces by the likes of Picasso, Courbet and Monet.

But the colossally rich and notoriously secretive Wildenstein dynasty is now facing unwanted publicity as the result of lawsuits from two women who claim to have been scorned by their in-laws.

Guy Wildenstein, the Franco-American patriarch, has been placed under formal investigation in France, the equivalent of charging a suspect in the UK, on suspicion of tax evasion. His nephew, Alec Jr, is being investigated over the same alleged offence. Le Parisien newspaper said the French tax authorities were claiming a total of €600 million (£515 million).

The dynasty’s woes were initiated by Sylvia Roth, an American model and