I agree with Scotz 100%
Tell your wife, the risk of upsetting her is MUCH less if it comes from you, and lord knows, these things always come out sooner or later. Plus it eliminates any chance of residual guilt on your part for not telling her.
I have been in this position, I would say that your safest bet is to assume the gf's intentions are not honorable. Right or wrong, that assumption in the long run is the safest for all. She has been out of your life for 10+ years, her friendship may be nice to have, but is it worth it? What would you gain? What would you feel if it were her, with a boyfriend walking back into her life?
If she makes contact again, say, it's been nice to see you again but you'd rather leave things as they were.

BORU