In 1670 he escorted the King's sister Henrietta of England, Duchess of Orleans, from France to England to negotiate the Secret Treaty of Dover between her brother and Louis XIV. Of the existence of the Treaty's secret clauses, notably that by which Charles II pledged to convert to the Roman Catholic faith, Sandwich, like the general public, was quite unaware. In the same year he was appointed President of the Privy Council Committee on Foreign Plantations; he had always had a keen interest in international trade, despite his notorious inability to keep his own finances in order.
