Moulting is a natural process which occurs in many animals, humans included. Many people use the term ‘shedding’ and the two are exactly the same process.
Dogs, including the Cavalier King Charles spaniel, undergo a process which results in a thicker coat growing in the winter and cold months, this provides effective cold and bad weather protection, keeping the dog warm and is a basic dog survival process.
When the weather improves, this coat is too heavy and warm, so the dog moults or sheds the excess hair so that he is not too warm or uncomfortable.
You would not want to wear a thick winter coat during the summer and the same if true of your Cavalier King Charles.
Moulting or shedding is just like the dog taking his coat off. It is normal.