Sigyn is the wife of Loki, making her princess of Asgard.
When Loki was young, he came to desire a wife, and admired Sigyn from afar. When he went to court her, she revealed that she was betrothed to Theoric. Loki arranged to have Theoric murdered but make it look like he was killed in battle, and then disguised himself as Theoric so that Sigyn and “Theoric” were eventually wed by Odin. At the end of the ceremony, Loki revealed his true form. Odin was furious, but Sigyn noted that as his wife, she was duty-bound to Loki for life. Odin made her the goddess of fidelity for her endurance, and banished Loki from Asgard.
In their marriage, Sigyn mothered two sons with Loki, Narvi and Váli, although both of them died young.
She is assumed to have died during the Ragnarok in Thor II #85. (x)