In later years the cathedral was destroyed , and the tombstone was lost , but it was found in 1859 ( it was being used to cover a well ) , and is now in the Palais des Beaux Arts museum in Lille . After the destruction of the cathedral the tombstone was lost , but it was found in 1859 ( it was being used to cover a well ) , and is now in the Palais des Beaux Arts museum in Lille .