Youtuber Alt Shift X brings us this Game of Thrones fan theory in which he suggests that Tormund Giantsbane may have had a love affair with Maege Mormont, the former leader of Bear Island and the mother of Lyanna Mormont. In the show however, Maege died while fighting for Robb Stark, probably at the Red Wedding, which also explains Lyanna’s hatred for the Boltons. “My mother wasn’t a great beauty or any other kind of beauty. She was a great warrior though,” Lyanna told Jon & Sansa in season 6, referring to her mother in the past tense.
In the books however, Maege is probably alive and also has several daughters whereas in the show, it appears she only had one. If Tormund had an affair with Maege, and with Bear Island near the Wildling Lands, he could very well be Lyanna’s father.
And Tormund even shared a story about having sex with a bear in the books- an abbreviated version of which was also included in the show (see above video). Did he mean Maege? You can watch the fan theory video below.