In Bart Gets Hit by a Car(7F10)
Prevouisly no one was sitting next to Mr Burns
When Mr Burns attorney is cross-examing Marge saying "Does the name Julius Hibert mean anything to you?".
Mr Burns appears to have a 'black' burns like character sitting to his left wearing a grey suit.
Then Mr Burns attoney is also sitting to his right while also standing up cross-examing Marge.
Later on Mr Burns is holding the wrist of the 'black Mr Burns'.
Finally Smithers it sitting to Mr Burns his left hand side.