 His proclamation included the title "true heir of Sweden" added at his mother's insistence since his paternal grandfather, Magnus IV, had been king of Sweden until forced to abdicate.Olaf was hailed as king in Scania, including the towns controlled by the Hanseatic league since the Treaty of Stralsund in 1370.Queen Margaret signed a coronation charter on behalf of Olaf, who was too young to rule until he came of age at fifteen.