Paul Anka has seen it all in his half-century in Hollywood ... and that includes Frank Sinatra 's schlong.

The legendary singer-songwriter joined us on "TMZ Live" Wednesday and we asked him about his new documentary, his upcoming Broadway show, his secrets to health and longevity, his legal beef with Michael Jackson , the story behind Sinatra's "My Way" ... and yes, Sinatra's penis. Getty

Paul made headlines this week when he confirmed Frank was very well-endowed ... and here, he hilariously explains how Sinatra's massive member got brought up in an interview that went viral.

Speaking of Sinatra, Paul tells us how he got the rights to the melody for "My Way" during his international travels back in the day ... and you won't believe the sweetheart deal he struck with the

See Full Page