During his seneschalcy, King Henry III of England, who was also the hereditary Duke of Aquitaine and Gascony, launched the a war against France.
On John's death that year he was released on the orders of the regent, William Marshal.
[1] Bémont has him continuing in office until the next known mayor, Pierre Béguey, was installed on 9 July 1242.
[2] Rostan was appointed on 22 September 1241, as Seneschal of Gascony,[3] replacing Henry de Turberville.
[4] Simon de Monfort, the Seneschal of Gascony, put down the factional fighting, arresting Rostan and sending him to England to appear before Henry III.