Birger (Swedish: Birger Magnusson; 1280 – 31 May 1321) was King of Sweden from 1290 to 1318. His reign was marked by unrest and civil strife; he was imprisoned by his brothers Erik and Valdemar following the "Håtuna games" in 1306, but when he tried to play them the same trick in Nyköping, there was an uprising that ended with Birger losing the crown and the execution of his 18-year-old son Magnus. Background. Birger was the son of King Magnus Ladulås and Helvig of Holstein. He was hailed king of Sweden when he was four years old.
https://en.wikipedia.org/wiki/Birger,_King_of_Sweden