Four colours are recognised: Blenheim (chestnut and white), tricolour (black/white/tan), black and tan, and ruby; the coat is smooth and silky.

[2] The Cavalier King Charles changed dramatically in the late seventeenth century, when it was inter-bred with flat-nosed breeds.

Breeders attempted to recreate what they considered to be the original configuration – a dog resembling Charles II's spaniel of the English Civil War period, when supporters of the king were known as Cavaliers.

[3][4] During the early part of the 18th century, John Churchill, 1st Duke of Marlborough, kept red and white King Charles type spaniels for hunting.

[6] In 1926, the American Roswell Eldridge offered a dog show class prize of 25 pounds of sterling silver each as a prize for the best male and females of "Blenheim Spaniels of the old type, as shown in pictures of Charles II of England's time, long face, no stop, flat skull, not inclined to be domed, with spot in centre of skull.

"[7] The breeders of the era were appalled, although several entered what they considered to be sub-par Cavalier King Charles Spaniels in the competition.

[7] The first standard was created, based on a dog named "Ann's Son" owned by Mostyn Walker,[8] and the Kennel Club recognised the variety as "King Charles Spaniels, Cavalier type".

[15] The Blenheim spot is also known as the mark of the "Duchess Thumb Print", based on the legend that Sarah Churchill, Duchess of Marlborough while awaiting news of her husband's safe return from the Battle of Blenheim, pressed the head of an expecting dam with her thumb, resulting in five puppies bearing the lucky mark after news that the battle had been won.

[7] Ruby Cavaliers should be entirely chestnut,[18] although some can have some white in their coats that is considered a fault under American Kennel Club conformation show rules.

[7] According to statistics released by The Kennel Club, Cavaliers were the 6th most popular dog in the United Kingdom in 2007 with 11,422 registrations in a single year.

[25] In 2009, the Cavalier was the 4th most popular breed in Australia with 3,196 registrations, behind only Labrador Retrievers, German Shepherd Dogs and Staffordshire Bull Terriers.

[26] In addition, there are also national breed clubs in Belgium, Canada, Czech Republic, Denmark, Finland, France, Germany, Netherlands, New Zealand, Norway, South Africa, Spain and Sweden.

Cavaliers are successful in conformation shows, obedience and agility and they also make wonderful therapy dogs due to their sweet, gentle natures.

[31] As they tend to regard all strangers as friends, members of the breed will usually not make good guard dogs.

However, owners have reported that through training their Cavaliers live happily with a variety of small animals including hamsters and gerbils.

[33] A 2024 UK study found a life expectancy of 11.8 years for the breed compared to an average of 12.7 for purebreeds and 12 for crossbreeds.

[34] A 2018 Japanese study of pet cemetery data found a life expectancy of 13.1 years compared to 15.1 for crossbreeds and 13.7 overall.

[39] Additionally, bad breeding increases the chance that a Cavalier will develop MVD, so it is important to find a responsible breeder who uses dogs with healthy hearts.

The health problems shared with this breed include mitral valve disease, luxating patella, and hereditary eye issues such as cataracts and retinal dysplasia.

In 2022, the Oslo District Court banned the breeding of Cavalier King Charles spaniels in Norway due to their propensity for developing health problems.

[46] Syringomyelia (SM) is a condition affecting the brain and spine, causing symptoms ranging from mild discomfort to severe pain and partial paralysis.

Scratching typical of SM is usually worse when the dog is wearing a collar, is being walked on a leash, or is excited, and first thing in the morning or at night.

[48] Not all dogs who show scratching behaviour appear to be in pain, though several leading researchers, including Dr. Clare Rusbridge in the UK and Drs.

Curtis Dewey and Dominic Marino in the US, believe scratching in SM Cavaliers is a sign of pain and discomfort and of existing neurological damage to the dorsal horn region of the spine.

[51] Severity of symptoms can range from mild, occasional falling to freezing to seizure-like episodes lasting hours.

The platelets in the blood of many Cavalier King Charles Spaniels are a combination of those of normal size for dogs and others that are abnormally oversized, or macrothrombocytes.

[54] Hip dysplasia is a common genetic disease that affects Cavalier King Charles Spaniels.

The grades 3–4 are most severe where surgery will most likely be needed to correct the problem to avoid the development of arthritis and lameness in the limb.

According to the Canine Inherited Disorders Database, the condition requires continual treatment and if untreated may result in partial or total blindness.

[62] Cavalier King Charles Spaniels may be predisposed to a form of congenital deafness, which is present at birth, due to a lack of formation or early degeneration of receptors in the inner ear, although this is relatively rare.