How to find the real class name from obfuscated ProGuard classname in my source code?

I got an email from Google about unsafe implementation of TrustManager with the only clue that the problematic code is in com.b.a.af class. Clearly that's the obfuscated name. How would I get the real class name from that obfuscated class name, in my own source code. Is there any way to lookup the mapping that ProGuard does? Thanks!