That happy, curious look on M'gann's face? It gets wiped straight off and replaced with confusion when she gets that response; she can feel how palpable his surprise is...And she hasn't heard anything like that from Robin for months. And a second later comes the realization that he looks, sounds, and psychic-wise feels different.

It's enough to get her to drop that mental link out of shock, as she does a skip backwards in the air out of surprise.

"You're not-" She stops short of saying 'Robin' because there is a certain resemblance. If nothing else, this person is really good at making super hero costumes, even if a few of the details don't look quite right.

"I-I know him. He's my uncle-" She blurts that out as she tries to find her mental feet again.