Season 3: Lagertha
In the beginning of season 3, Lagertha is told by a Seer that she will not be able to have anymore children and also learns that her death has already been decided by the gods.
She then travels to Wessex with the intention of creating a thriving settlement. When she is there, King Ecbert shows interest in her and her plans for the settlement. The two then have a love affair, but any hope of Lagertha getting a new love interest is dashed when Ecbert betrays her by sending men out to kill the settlers after she leaves.
And she finds even more problems at home when she finds that her second in command Kalf has taken over her earldom. Surprisingly Lagertha agrees to marry him after he saves her life at the Paris siege, but not without her promising him that she will kill him eventually for usurping her.