Which English king is known to have had at least 21 illegitimate children?

Henry I (c. 1068 – 1 December 1135), also known as Henry Beauclerc, was King of England from 1100 to his death in 1135. He was the fourth son of William the Conqueror and was educated in Latin and the liberal arts.

On 11 November 1100 Henry married Matilda, the daughter of Malcolm III of Scotland. Matilda proved an effective queen for Henry, acting as a regent in England on occasion, addressing and presiding over councils, and extensively supporting the arts. The couple soon had two children, Matilda, born in 1102, and William Adelin, born in 1103.

Henry had a considerable sexual appetite and enjoyed a substantial number of sexual partners, resulting in a large number of illegitimate children, at least nine sons and 13 daughters, many of whom he appears to have recognised and supported. It was normal for unmarried Anglo-Norman noblemen to have sexual relations with prostitutes and local women, and kings were also expected to have mistresses. Some of these relationships occurred before Henry was married, but many others took place after his marriage to Matilda. Henry had a wide range of mistresses from a range of backgrounds, and the relationships appear to have been conducted relatively openly.