Regnal years of English monarchs Britain), from 1066 to the present day. These are official "de jure" dates, and may or may not coincide with whether a particular king had "de facto" power or not at that time. For example, as the Commonwealth era was suppressed in the official record, the regnal years of Charles II are measured from 30 January 1649 (the day his father Charles I was executed); as a result, when Charles II actually became king, on 29 May 1660, he was already in his 12th regnal year. (For the "de facto" tabulation of English rulers, see any conventional list of English
Treaty of Copenhagen (1660) had already agreed with England that preventing the western and eastern shore of Øresund from being controlled by the same country would in turn prevent future raises of the Øresund toll, which would cause disruption in the Dutch and English Baltic trade. In addition, Cardinal Mazarin threatened a French invasion of the Netherlands if it were to assist Denmark against Sweden. When learning of Charles' death in February 1660, Frederick immediately proclaimed the Treaty of Roskilde null and void. This caused great alarm to the Swedish mediators, but their French and English counterparts assured them that if Sweden were to