John of Gaunt
John fathered five children outside marriage, one early in life by a lady-in-waiting to his mother, and four by Katherine Swynford, Gaunt's long-term mistress and third wife. These were surnamed Beaufort (after a former French possession of the Duke). The Beaufort children, three sons and a daughter, were legitimised by royal and papal decrees after John and Katherine married in 1396. Their half-brother Henry IV added a later proviso that they were barred from inheriting the throne.