Lorelei fist seducing Thor and later Loki. From The Might Thor #358, written and drawn by Walter Simonson.
(You can click for enlargement, but the order is off because I wanted the 2 lower pages next to each other in the picset)
Lorelei has been trying to seduce Thor ever since the start of Simonsons run, with limited success. In issue 357, Loki gives Lorelei a bottle with a scent that would make Thor her love-slave. In exchange he wants Lorelei to convince Thor to grand him the rulership of Asgard. On the last page of the issue she smashes the bottle, releasing the magical green vapors.
Meanwhile, Amora the Enchantress was angry with her sister Lorelei for not assisting Asgard in the war against Surtur. She decided to punish her by enchanting the great scepter of Odin, which had been laying around in the rubble ever since the fight. The first person to pick it up would be the recipient off a spell of Lorelei-attraction. She figured it would probably be Loki, and was proven right (although Heimdal was only a few yards away, apparently also salvaging stuff).
After spending some time with Thor, Lorelei travels back to Asgard to discuss the fine print of her deal with Loki, and at first sight of him falls victim to the spell. Neither of them realizes this.
Shortly after, Thor gives in to Lorelei’s demands about making Loki king. He decides to pay him surprise visit to relay the happy news as soon as possible. Doing so he catches Loki in bed with Lorelei. Initially this upsets him, but doesn’t break the spell. It takes some off-screen exhibitionistic actions of Lorelei to enrage him enough to temporarily overrule his magical enslavement, and in this state he threatens Loki into lifting it from him entirely.
Thor departs, leaving a very grumpy Loki with a still enamored Lorelei.