Eric "XII" of Sweden was a rival king of Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

 of his father Magnus IV

Magnus IV of Sweden

Magnus Eriksson as Magnus IV was king of Sweden , including Finland, as Magnus VII King of Norway , including Iceland and Greenland, and also ruled Scania . He has also vindictively been called Magnus Smek...

 from 1356 to his death in 1359. He was married to Beatrix of Bavaria

Beatrix of Bavaria

Beatrice of Bavaria ; Swedish: Beatrix ; was Queen of Sweden by marriage to King Eric XII, who co-ruled with his father, King Magnus IV....

, daughter of Louis IV of Bavaria

Louis IV, Holy Roman Emperor

Louis IV , called the Bavarian, of the house of Wittelsbach, was the King of Germany from 1314, the King of Italy from 1327 and the Holy Roman Emperor from 1328....

.

In 1343 Eric and his brother Haakon

Haakon VI of Norway

Haakon VI of Norway was King of Norway from 1343 until his death and King of Sweden from 1362 until 1364, when he was deposed by Albert of Mecklenburg in Sweden.-Background:...

 were elected heirs of Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

 and Norway

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

, respectively . That Haakon got the Norwegian throne in 1355 (causing the union between Norway and Sweden to split) while Eric didn't get any position in the Swedish council might have affected his choice to lead a rebellion against his father in 1355. In 1357 the rebellion had forced Magnus to share Sweden with his son Eric who got to rule most of Southern Sweden and Finland

Finland

Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...

. Sweden was reunited again in 1359 when father and son became reconciled, and co-ruled Sweden until Eric's death a few months later. While dying Eric accused his mother Blanche of Namur for poisoning him. Quite soon after the death his wife Beatrix died too. It is generally believed that they died of the plague

Black Death

The Black Death was one of the most devastating pandemics in human history, peaking in Europe between 1348 and 1350. Of several competing theories, the dominant explanation for the Black Death is the plague theory, which attributes the outbreak to the bacterium Yersinia pestis. Thought to have...

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