The Wedding of Iron Man - S1-E13
Plot hole: When Mandarin is concluding that Tony Stark and Iron Man are one and the same, he is watching video footage of when he had Tony Stark captive, and Tony first constructed the Iron Man armor and used a dummy that looked like himself in order to fool Mandarin into thinking that Iron Man was rescuing Tony Stark from captivity. If Mandarin had video footage of Tony Stark in that room where he organized his own rescue, then he also would have had footage of Tony Stark constructing the dummy of himself in the first place, and thus would have known Stark was Iron Man from the get go. (00:13:06)