His father was a son of King Valdemar II of Denmark (1170–1241)[2] born in the non-wedded (but probably engagement-promised) espousing with a widowed Swedish lady, Helena, daughter of Earl Guttorm.
In 1241 Svantepolk got designated to inherit the Swedish landed properties of his grandfather King Valdemar II.
Valdemar's heirs agreed that the troubles in preceding decades, caused by various Swedish regime's opposition towards the monarch of Denmark owning property inside borders of Sweden, is better to end totally.
For this, making a clear separation, the young Svantepolk, son of illegitimate family branch, gets designated to be a Swede and to live as loyal subject/vassal of Sweden.
Svantepolk is the second husband (since c1250/1253) of Benedikta Sunadotter, lady of Söderköping et alii (floruit 1244-1261; died: years after 1261), daughter of Sune Folkason of 'Ympseborg fame' (d. 1247), a grandson of riksjarl Birger Brosa (d. 1202).
Benedikta's mother was Helena Sverkersdotter, heiress of Visingsö et alii, the daughter of King Sverker II of Sweden and his (second) wife Benedicta Ebbesdotter of Hvide (d. ca.
[4] [5][6] [7][8] As Benedikta Sunadotter had earlier been taken as tool for political opposition by her abductor Laurens Pederson (died in c1249 in exile in Norway), Benedikta's marriage with Svantepolk is presumably arranged by riksjarl Birger and king Eric's camp for neutralizing the possibility of using her as symbol to claim the Swedish throne in name of Sverker-dynasty heritage.