For many centuries, small breeds of Spaniels have been popular in the United Kingdom. In the eleventh century, in the reign of King Canute, it was illegal to hunt with any dog that could not fit through a gauge that was but eleven inches in diameter. So, the 'birth' of the Toy Spaniel in the United Kingdom. Some centuries later, Toy Spaniels became popular as pets, especially as pets of the Royal family. In fact the King Charles Spaniel was so named because the Blenheim was the children's pet in the houshold of King Charles the First. In the beginning of the 1900's, an American offered twenty-five pounds as a prize to any King Charles Spaniel 'of the old-fashioned type' with a longer nose, flat skull and a spot in the middle of the forehead, commonly called 'the kiss of Buddha'. So, the breed was developed by selective breeding of short-snouted King Charles Spaniels (also known as English Toy Spaniels).
The breed has four recognized colors: Blenheim (reddish brown and white), Black and Tan (black and reddish brown), Ruby (reddish brown), and Tricolor (reddish brown, black and white).
The breed is highly affectionate, and some have called the Cavalier King Charles Spaniel 'the ultimate lap dog'. The dogs require a great deal of human companionship, and do not do well if left alone for long periods of time. The breed suffers from a number of congenital defects, most significantly, mitral valve disease. This condition can begin to emerge at an early age, and is present in many Cavalier King Charles Spaniels by 5 years of age. Responsible breeders are attempting to breed only from dogs that exhibit a later onset of the disease. The increasing popularity of the breed has led to breeding of the Cavalier King Charles Spaniel in puppy mills. Puppy mills are located around the world and are sold in the United States through brokers . Those interested in purchasing a Cavalier King Charles Spaniel should be very cautious about selecting a breeder and should never purchase this breed from a pet store.
Two breed clubs are found in the United States: the Cavalier King Charles Club USA and the American Cavalier King Charles Spaniel Club. The latter club is the breed club of the American Kennel Club.