Starscream continues to look baffled, until he remembers his initial observation of this stranger... how similar yet unlike he looks to a very certain someone... And then realization dawns on him, and it's horrifying.

"No, you can't be-" he glances down at the Autobot badge on Megatron's chest. "That is absurd," he says flatly. What he's referring to specifically isn't really clear. He's just baffled, and kind if dismayed.