You thought Snape was enigmatic, hard to figure out? Don’t count on Alan Rickman to help you — because once he makes a promise, he keeps it. When we caught up with Alan in London for “Sweeney Todd,” we had to ask what he thought of what’s finally revealed about Snape in “Deathly Hallows,” and he refused to spill. “There may have been people who have not read that book,” he insisted. “I won’t talk about it just in case somebody flips some channel, some computer screen, and they haven’t got that far.”

Guess we should have brought some Veritaserum to the interview, but Alan did give up just “one tiny thing” — that author J.K. Rowling had let him in on a bit of the secret before he filmed his first scenes in the Harry Potter series.

“I had one tiny piece of information right at the beginning,” he revealed. “Because I said to her, ‘You have to tell me something, or else I can’t play this.’ It didn’t tell me how to play him, but it told me who he was a little bit.”

So what did she give up? He won’t say. “I swore to her I never would tell until it’s all done and dusted,” he said. Was it the end? “I never knew what the end was.” Was it who Snape really was? “I never knew who he was.” Was it about … Lily? “I’m not telling you anything!” he said — and was that perhaps a sense of glee we noted? Glee because we hit on a right note, or because he was having so much fun keeping the secret?

“I’m so aware of the kids, and this is for them,” he explained. “There are so many little faces sunk deep into books, and sometimes it’s still a fog because it could take a while for them to read them, and you don’t want to spoil it for anyone.”

Ok, we can accept that. But he’s got to be looking forward to “Half-Blood Prince,” right? “Well,” he relented with a sneaky smile, “maybe.”