Match, as you entered the Citadel - a guard attacked you, right? And he dropped a key and an armour => there the speech option with the DK came to disguise yourself with this guard's armour (please, read your dialogue log - or did you exit this convo without using all speech options?) - and General Bram's/Bran's note on the table was a clue to be careful. You unlocked the door? Then the next warning came => sneak past the hostile DK.
Kiya
