Survivors of the failed uprising then fled to Brittany, where they openly supported Henry Tudor's claim to the throne. On Christmas Day in 1483 at the Rennes Cathedral, Henry swore an oath to marry King Edward IV's daughter, Elizabeth of York, and thus unite the warring houses of York and Lancaster. Henry's rising prominence made him a great threat to King Richard III, and the Yorkist king made several overtures to Duke Francis II to surrender the young Lancastrian. Francis II refused, holding out for the possibility of better terms from the King. In mid-1484, Francis was incapacitated by one of his periods of illness, and while recuperating, his treasurer, Pierre Landais, took over the reins of government. Landais reached an agreement with King Richard III to send Henry and his uncle Jasper back to England in exchange for a pledge of 3,000 English archers to defend Brittany against a threatened French attack. John Morton, a bishop of Flanders, learned of the scheme and warned the Tudors in time. The Tudors then managed to separately escape, hours ahead of Landais' soldiers, across the nearby border into France. They were received at the court of King Charles VIII of France, who allowed them to stay and provided them with resources. Shortly afterwards, when Francis II had recovered, he offered the 400 remaining Lancastrians, still at and around the Château de Suscinio, safe-conduct into France and even paid for their expenses. For the French, the Tudors were useful pawns to ensure that King Richard III did not interfere with French plans to acquire Brittany. Thus, the loss of the Lancastrians seriously played against the interests of Francis II.