All purebred dogs have a written standard to which a breeder strives to uphold. This standard is something a prospective owner should read before they choose the kind of dog they would like to have. These standards are all available via the Canadian Kennel Club when you search for the breed you want. The following information is from the breed standard but has been shortened to give a brief overview. I have included a link to the detailed standard at the bottom and encourage any prospective family to read it.
The Cavalier King Charles Spaniel, briefly put, is a part of the Toy group. They are descended from the Toy Spaniels of Europe and have been recorded as being present in the court of Queen Mary I but were given their name by King Charles II in the 17th century.
They are an active breed known for loving to cuddle but they are not simply couch potatoes. They share a history with the rest of the spaniels and can often be seen chasing birds. They are not street savvy and will give chase without any thought to danger (like cars). It is best to keep a Cavalier on a leash for this reason especially in cities or areas where they could be in harm's way.
Height: 12-13 inches. Weight: 14-18lbs. Small variations in both weight and height are permitted. Coat: Long, silky and free from curl although a small wave is permitted. Colors: Only four colors are accepted by the CKC and those are :
Blenheim - Brown with chestnut red markings
Tricolor - Jet black markings on a white background. Tan points above eyes and on cheeks, inside the ears and under the tail
Black and Tan - Jet black with rich tan markings over the eyes, on cheeks and muzzle, inside the ears, on throat and chest, on forelegs from knees to toes, on the inside of the hind legs also extending from hocks to toes, on the underside of the tail and surrounding the vent.