system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] How and when did Thor find out about Loki being an adopted frost giant, and how did he react to that revelation?

At the end of Thor, Loki knows the truth, and Frigga knows that Loki knows, but at no point does Thor find out the whole truth. In The Avengers, Thor says "He is adopted," so he must have learned the truth sometime between the events depicted onscreen.

Did Odin and Frigga have a civil heart to heart family meeting with Thor? Did Thor have feelings of confusion and betrayal about the lies that he had been raised believing? How did that all go down?
gpt
Odin probably just told Thor in between the events of Thor and The Avengers. It seemed like it was kept a secret more for Loki's sake than anyone, so once he found out it wasn't really a secret anymore. By the time of Thor: Ragnarok it appears to be public knowledge.