He was in his office when his secretary put someone through, an old-sounding guy who sounded really out of breath. He said: "Are you S---- F--------?", to which my dad said yes, then the old guy started rambling about how hard it was to get though to him on the phone, after finding him on the company's website, blah blah blah.
Anyway, ater a minute of stuttering incoherence, he said: "S-----, I have something to tell you. I'M YOUR FATHER."
My dad was rather taken aback, but after a few minutes managed to persuade this guy that he knew his background very well, and looked a lot like his father and siblings. The man on the phone went all quiet then just said: "I've made a terrible mistake" and hung up.