King James II
James was not only William's uncle, he was also his father-in-law.
In 1688, when William's army of invasion reached Axminster, John Churchill, 1st Duke of Marlborough, and many other officers and soldiers deserted from James IIs army and defected to William's army. James knew that the Duke of Marlborough owed him a great deal for his patronage and friendship over the years, so when James learnt that the even the Duke of Marlborough was among the deserters, James fled to France.