"Dawn of the Dukes" will be the second DLC for Age of Empires II: Definitive Edition coming “this summer” (i.e. at an yet unspecified time in 2021). So far the information about the new release is scarce, but the confirmed new features include co-op mod and new campaigns with a focus on “Eastern Europe”.
No new civilizations have been announced yet.
…And I can’t help but imagine the “Duck Hunt” dog barking “Down with the Ducks” at my screen for some reason.