During the reign of King William III and Queen Mary II, the long nosed style of spaniel went out of fashion. The Pug was the favored dog at the time in the Netherlands, and with William's Dutch origin, they became popular in England too. At this time interbreeding may have occurred with the Pug, as the King Charles took on some Pug-like characteristics.
After the king's death, the Duke of Marlborough took over the breed. During the early part of the 18th century, John Churchill, 1st Duke of Marlborough kept red and white King Charles type spaniels for hunting. The duke recorded that they were able to keep up with a trotting horse. His estate was named Blenheim in honor of his victory at the battle of Blenheim. Because of this influence, the red and white variety of the King Charles Spaniel and thus the Cavalier King Charles Spaniel became known as the Blenheim.
This is just the beginning of their history in Europe but let's jump ahead to their history here in America. They are seen in many early American paintings. But the first recorded Cavalier King Charles Spaniel in United States was imported in 1946. Not long after a Cavalier club was formed and then after the breed became established here in America in 1995 The American Kennel Club (AKC) officially recognized Cavalier King Charles Spaniels as a breed.