The king made several failed attempts to escape, one time famously getting stuck in a castle window. He also had letters smuggled out, most of which were intercepted, which he signed 'J' to disguise his identity (donkeys operating the castle's water-well have subsequently been given names beginning with 'J'). In September 1648 he discussed the Treaty of Newport with the Presbyterian faction of Parliament, which would have granted him a constitutional monarchy. However, he had no intention of accepting its restrictions, and so also conspired for the Scots to invade England on his behalf. This led to his eventual execution on 30 January 1649.