I think the number of monarchs of the UK/England that were faithful could be counted on less than 10 digits. And that takes into account that it was expect of the Kings to have mistresses.
Infidelity by a queen would be a different matter...which is why Ann Boleyn and Catherine Howard were executed (although Ann was probably innocent). That risked putting on the throne a man who was unrelated to the earlier members of the dynasty.
Isn't there some speculation that Queen Victoria was the product of adultery and that that's how the hemophilia trait entered the British royal family?
fidelity ping