Donne was their third son who entered, probably in his late teens, the service of the Duke of York, father of Edward IV. He may have done so through the patronage of the leading Yorkist in South Wales, William ap Thomas, also an Agincourt veteran and father of Donne's contemporary William Herbert, 1st Earl of Pembroke (1423-1469). Donne is recorded as having fought in France for the Duke, which must have been before 1447. It is from this and his apparent age in the Memling that his birth in the 1420s is estimated. He also fought for the Duke in England, and in the late 1440s in Ireland.