In 1538, Antoine claimed the titles of Duke of Guelders and Count of Zutphen upon the death of Charles of Egmond, but was unable to gain possession of them. He married his heir, Francis to Christina of Denmark, niece of Charles V, in 1541, and with the Treaty of Nuremberg (26 August 1542), Antoine obtained from Charles V the independence of the Duchy of Lorraine. He interceded at the start of Francis and Charles' war in 1542 as a peace envoy, visiting Charles in person, but due to gout sent his heir to Francis. In fact, Antoine asked his niece, Mary of Guise, to send him a Scottish hackney horse which he hoped would be easier to ride with his gout.