Your friend may have seen it on the internet--that is to say, in a search through one of the P2P file sharing programs, like Gnutella or whatever, but the labels on those files often have nothing to do with who is on them--Someone told me that they once did a search for "Kung-Fu Fighting" and came up with versions by Jimi Hendrix, the BeeGees, and Simon and Garfunkel, only they were all the original, by Carl Douglas.

A metal guitarist by the name of Chris Impelliteri recorded a really outstanding instrumental of "Over the Rainbow" an few years back--it is all over the P2P filesharing networks, but it is always attributed to Yngwie Malmsteen or Eric Clapton--it never has his name attached--in fact, there is a note on one of the Yngwie Malmsteen sites that says that Yngwie never recorded OTR, and that all the P2P files of it with his name on them are really Chris Impelliteri--

So it might be BB King with someone that sounded(to the file poster) like Billie Holiday, or it might not have been BB King, either--maybe it was T-Bone Walker--