Well, that was a bit of a surprise, as Roger had thought he knew her from the Ministry. He knew everyone that had been on his team, and she hadn't been. And he couldn't place her on any other team right off. But she knew him from then? Times like these were when Roger sometimes questioned his rather lack of scruples, as there were a many number of possibilities of who she might be. Though, from her actions, he got the feeling that they had never actually been together. So, therefore, that could only mean one thing.
"You're... a couple years younger than me, aren't you?" He knew she wasn't in Cho's year, given that he'd hung out with Cho a lot, and therefore had hung out with Cho's frinds, which was pretty much everyone in her year. So, she had to be younger.