Pretty sure that's a Shakespeare reference

Possibly, but:

Archer, season 3, episode 10 - "Crossing Over"

Colnel Jakov defects to America after finding out that he has been userped by Barry Dylan. While learning this in what was once his own office, Jakov also finds out that his once faithful subordinate, Brute, has happily embraced working for Barry.

Jakov: "Et tu, Brute?"

Brute: "Et me, buddy"