In 1670, he was appointed as conservator of the royal collection in Potsdam. In 1671, when Van Uylenburgh tried to sell 13 paintings to
Frederick William, Elector of Brandenburg, Fromantiou successfully advised the Elector to send 12 pieces back as forgeries. Fromantiou claimed the paintings were copies of Italian ones, and he could point out the originals in Holland. Included in the 51 people involved in the expertise, was
Johannes Vermeer. ==Personal life==