In a constitutional monarchy, who is the considered the head of state with real political power?

Legislation or Parliament

A constitutional monarchy has a monarch who leads with a legislative branch elected by the people.

A constitutional monarchy usually has a legislation or parliament with an elected leader who holds the majority of the political power. The monarch works with the legislative branch or will hold only traditional power. Great Britain is an example of a constitutional monarchy where the king/queen holds only a traditional place in the government and offers their opinion in political matters, but real political work takes place within Parliament and with the Prime Minister.

In the oldest form of government, which is the constitutional monarchy, the head of state is the king and queen however the ability to make and pass laws or legislation is in the hands of an elected Prime Minister.