Charles, like all kings, was styled by a royal title, which combined all his titles into one single phrase.
This was:
We Charles, by the Grace of God King of Sweden, the Goths and the Vends, Grand Prince of Finland, Duke of Scania, Estonia, Livonia and Karelia, Lord of Ingria, Duke of Bremen, Verden and Pomerania, Prince of Rügen and Lord of Wismar, and also Count Palatine by the Rhine, Duke in Bavaria, Count of Zweibrücken–Kleeburg, as well as Duke of Jülich, Cleve and Berg, Count of Veldenz, Spanheim and Ravensberg and Lord of Ravenstein.

The fact that Charles was crowned as Charles XII does not mean that he was the 12th king of Sweden by that name.
Swedish kings Erik XIV (1560–1568) and Charles IX (1604–1611) gave themselves numerals after studying a mythological history of Sweden.
He was actually the 6th King Charles.
The non-mathematical numbering tradition continues with the current King of Sweden, Carl XVI Gustaf, being counted as the equivalent of Charles XVI.
Charles, like all kings, was styled by a royal title, which combined all his titles into one single phrase. This was:
We Charles, by the Grace of God King of Sweden, the Goths and the Vends, Grand Prince of Finland, Duke of Scania, Estonia, Livonia and Karelia, Lord of Ingria, Duke of Bremen, Verden and Pomerania, Prince of Rügen and Lord of Wismar, and also Count Palatine by the Rhine, Duke in Bavaria, Count of Zweibrücken–Kleeburg, as well as Duke of Jülich, Cleve and Berg, Count of Veldenz, Spanheim and Ravensberg and Lord of Ravenstein.
The fact that Charles was crowned as Charles XII does not mean that he was the 12th king of Sweden by that name. Swedish kings Erik XIV (1560–1568) and Charles IX (1604–1611) gave themselves numerals after studying a mythological history of Sweden. He was actually the 6th King Charles. The non-mathematical numbering tradition continues with the current King of Sweden, Carl XVI Gustaf, being counted as the equivalent of Charles XVI.
Charles XII of Sweden