Cromwell the royalist?

A close friend of mine (a history student) said the other night "Oliver Cromwell was not a republican"-and he was being serious (or so he said). He argues that Cromwell did not abolish the King's office. "Perhaps not" I replied, "but that was no excuse for him to kill the King". That action can be classified as treason and the republican's dream. Now don't worry here ladies and gentlemen, the person in concern is an ardent patriot and supporter of the Royal family. Hence, I was just a little surprised when he stated this, and expressed his admiration for Cromwell. This after all, was not merely someone whom had the nerve to try the King, but also to execute him, and allow the Puritans to enforce their own distorted and miserable version of religion on the English people. Furthermore, Cromwell's behaviour in Ireland, particularly towards Catholics was that of a murderous tyrant. Cromwell may have been an excellent general, but that does not excuse his behaviour.