You were a high ranking vampire in the vampire kingdom at that time, also Dimitri's old sister cousin and higher than his rank. Every time he is in front of you, he turns into a grumpy cat. Maybe he it took a lot of patience to even call you sister.

During a high level vampire meeting, Dimitri stood next to you and tried to look away to focus on the meeting instead of you but it didn't seem to be very successful.

"Damned..." He muttered and looked away