The story you describe shares several elements with the story of the shield-maiden Brunhild and King Gunther (and the legendary Siegfried) in the The Song of the Nibelungs, a German epic poem.
Here's a quick summary of the relevant part of the story from Wikipedia:
When Siegfried and Gunther arrive at Isenstein, Brunhild initially assumes that Siegfried is the suitor, but immediately loses interest in him once he claims that he is Gunther's vassal. With Siegfried's help, Gunther is able to accomplish all the feats of strength; although Brunhild initially looks like she might renege on the agreement, Siegfried quickly gathers his men from his kingdom in Nibelungenland and brings them to Isenstein. Gunther and Brunhild then agree to marry. The heroes return to Worms with Brunhild, and Siegfried marries Kriemhild at the same time that Brunhild marries Siegfried. Brunhild cries seeing this however, believing that the royal princess Kriemhild has been married to a vassal. On her wedding night, when Gunther attempts to sleep with Brunhild, Brunhild quickly overpowers Gunther, tying him up by his hands and feet with her belt and leaving him hanging on a hook until morning. Gunther is forced to rely on Siegfried again, who takes Gunther's shape using his Tarnkappe and is only able to subdue Brunhild due to the Tarnkappe granting him the strength of twelve men. Gunther is secretly present during all of this, and is able to confirm that Siegfried did not sleep with Brunhild. Once Siegfried has subdued Brunhild, Gunther takes Siegfried's place and takes Brunhild's virginity, which results in the loss of her superhuman strength. As a trophy, Siegfried takes Brunhild's ring and belt, which he later gives to Kriemhild.
Wikipedia contributors. (2019, May 29). Brunhild. In Wikipedia, The Free Encyclopedia. Retrieved 14:15, June 5, 2019, from https://en.wikipedia.org/w/index.php?title=Brunhild&oldid=899285895
The Tarnkappe is a cloak of invisibility in German folklore.