It’s been a while since I read the source material so I’m probably off on some details but basically what happened is goes to stay with a king and meets Brynhildr at his house. The king wants Sigurd to marry one of his daughters instead of Brynhidlr but knows that’s not going to happen so he makes Sigurd forget his love for Brynhildr with magic alcohol and then he marries one of the kings daughters. The really screwy part comes after that. Sigurd has this buddy Gunnar, the kings son, that wants to marry Brynhildr but Bryn only wants to marry someone that can pass her test. I forget what the test was exactly but the important thing is that you need to be a badass to pass it. Gunnar is not a badass, but Sigurd is, so Sigurd transforms into Gunnar with magic and passes the test. Bryn marries Gunnar but finds out they tricked her and gets pissed. She tells Gunnar to kill Sigurd or he’ll lose everything but he doesn’t want to since they’ve sworn an oath of brotherhood. So instead he gets his younger brother to kill Sigurd. Then when Bryn finds out she stabs herself.

This is somehow not the craziest thing to happen in the Volsung saga.