The real Mandarin was Killian.
Great to see Trevor back
Sort of, there's a lot of work arounds to that. One that he had no connection to the 10 rings from the first film who were meant to tie into the mandarin at some point. When Killian said he was the Mandarin it's more likely he meant figuratively, that he wrote and created the Mandarin that Slattery played and he caused all the attacks so HE in that way was the mandarin that people were afraid of. That how I took that. There's still a way that a more traditional mandarin could exist in the MCU and Killian used like a legend of him to influence his figure.