My friend has a King Charles Cavalier. Angus stays with them when I am at work. Their dog is now 6 and Angus only 2 and a half. When we first got Angus, Bertie (their dog) towered over him. Now, of course, Angus is much bigger. They play fine, and Angus even defends Bertie, growling at dogs who are agressive to Bertie. Angus, otherwise is so so placid and loving. But sometimes Bertie gets knocked aside when they are both trying to get out of the back door at the same time, but he would never hurt him. I think you will be fine. Take care