While the Horrible Histories monarch song names the majority of English monarchs from William the Conqueror to Queen Elizabeth 2nd, it should be noted that there were English monarchs before William 1st. The first to be called King of all England was an Anglo Saxon prince named Athelstan. He was the son of King Edward the Elder and his first wife Ecgwynn.
Athelstan was brought up by his aunt Athelflaed, Lady of the Mercians and it was at Mercia where Athelstan was elected king of Wessex and Mercia. Athelstan had a sister who married the Viking ruler of the Northumbrians, Sihtric. Sihtric had control of the west and east of Britain and when he died, Athelstan inherited it in 927. He was made King of the English, in other terms, the first King of all England. He was one of the greatest Anglo-Saxon kings but when he died childless and a bachelor (a person who isn't married) in 939AD, the role was taken over by King Edmund 1. Over time there have been many royal households but today, England's royal house is the House of Windsor with the current monarch being King Charles III.