The retired couple who sold the mask to an antiques dealer for €150 is now suing in the southern French town of Alès, alleging that the dealer knew of the items value and deliberately underpaid them, The Times reports.

Frédéric Mansat-Jaffré, lawyer for the couple, said: “They would never have sold the mask at that price if they had known it was a very rare piece.”

Meanwhile, activist group Gabon Occitanie has launched its own legal proceedings arguing that the mask should never have been considered the couple’s property in the first place.

It was brought to France by the husband’s grandfather, a former colonial governor. Gabon Occitanie argues that it should be returned to Gabon.

“This family feel they have been cheated by a second-hand dealer, but really these two parties are disputing an object that does not rightfully belong to them,” campaigner Paul-Henri Gondjout Mbone Nze said.