Beatrice of Swabia

Already in 1203, King Philip attempted to betroth Beatrice to the nephew of Pope Innocent III, in order to gain the support of the Roman Curia. However, his plans failed and the rivals continued to fight. In 1207 Philip made an attempt to reconcile with Otto by offering him the hands of his daughter. Though Otto's strategic position had become unfavourable, he did not accept until Philip on 21 June was killed by the Bavarian count palatine Otto VIII of Wittelsbach. Otto of Wittelsbach, who had to dissolve his former engagement with Philip's daughter Kunigunde, had asked for the hand of either Beatrice or one of her three younger sisters in compensation. His request had been denied and he reacted violently. Beatrice was orphaned, when her mother Irene, renamed Maria, fled to Hohenstaufen Castle and died there on 27 August after delivering her youngest child.

Otto IV, suspected of being involved in the assassination, had by this point lost the support of his two main allies, Pope Innocent III and King John of England. He had been forced to retire to his hereditary lands near Brunswick in Saxony. However, the murder of Philip left him the only King of Germany. He took advantage to make amends with the remaining members and supporters of the House of Hohenstaufen and finally accepted late Philip's offer. Their new alliance was sealed with the betrothal of Beatrice to Otto IV.

On 11 November 1208, Otto IV was again elected King of Germany in Frankfurt. This time he was supported by members of both sides of the previous civil war. He was crowned Holy Roman Emperor by Pope Innocent III on 4 October 1209. Beatrice was only eleven years old and remained betrothed to Otto IV, approximately thirty-four years old.

As the bride was related to the Welf dynasty by her great-grandmother Judith of Bavaria, a papal consent had to be obtained, granted by Pope Innocent III in return for donations to the Cistercian abbeys of Walkenried and Riddagshausen. They were married in Nordhausen on 22 July 1212. The bride then was fourteen years old and the groom about thirty-seven.

The marriage with the granddaughter of late Emperor Frederick Barbarossa helped to reinforce Otto's position after Philip's nephew Frederick II, Beatrice's cousin, had been elected anti-king a year before. However, Beatrice soon fell sick and died only nineteen days after the marriage. She was childless at the time of her death.

Beatrice was buried in Brunswick Cathedral. A few weeks later, Frederick II arrived in Germany and on 9 December was crowned king in Mainz Cathedral. Otto IV was deposed and died in retirement at Harzburg Castle.