Talk:Shadow Play - Part 2/@comment-1031724-20180515201251/@comment-29981995-20190604200135

We don't know who told him, or how he was later able to get letters from Cozy Glow later on; it's an annoying plot hole that you can bet isn't going to be addressed now that the two are out of Tartarus. At any rate, Celestia certainly seemed to believe that he was aware of Cadance's ascension but not Twilight's. I would also say his reaction to Twilight was surprise, but definitely mingled with annoyance/anger at Discord for not disclosing the information to him.

Going back to the original post, I believe Tirek should actually come before the Sirens; in Legends of Magic Star Swirl mentions his defeat when Stygian comes to recruit him.