English Toy Spaniels vs. King Charles Cavaliers
The basic differences between the two breeds.
ET's or Charlies have short pushed-in faces and noses as compared to a Cavalier nose, which is about 1 inch from stop to tip. English Toy Spaniel ears should typically be set low to accentuate the domed head and Cavalier ears should be set high to accentuate the flat appearance of the skull. Note, however, that some Cavaliers have lower earsets than preferred and some ET's have higher earsets than preferred, so focusing on the roundness of the head and nose placement will probably help the most in this comparison.
ET's tails are typically docked and Cavalier tails are typically undocked and left long. Cavaliers are also slightly larger.
Both breeds come in the exact same colors, which share similar but not identical names.