A Cavalier King Charles Spaniel has a longer muzzle than their King Charles counterparts. The King Charles Spaniel has a much flatter muzzle and they have distinctly domed heads whereas Cavaliers have much flatter heads. Cavaliers have a strong scissor bite whereas a King Charles Spaniel’s jaw is slightly undershot. Additionally, Cavaliers tend to be slight larger than their King counterparts. Their temperaments also differ- Cavaliers are a bit more outgoing where the Kings are a little more reserved.