Who is it (Sport)

In 1999,
Alex Ferguson foes to the Arsenal training camp and says to Arsene Wenger, "Arsene how come yor players seem so much fitter and sharper than mine?" Arsene replies," well it is because i ask them a question everyday - watch. Dennis come over here" Dennis Bergkamp trots over and says "yes boss". "Dennis it is your fathers son but not your brother, who is it?" "It is me boss" replies Dennis. "Very good, off you go now", retorts Arsene.
Having seen this Alex goes back to Manchester United and calls over David Beckham. "david it is your fathers son but not your brother who is it?" David pauses for a momment and then says, "this is a tricky one gaff can i have the evening to mull it over?" "course you can" replies Alex. So david goes home and thinks i know i willl ring Jaap Stam he seems like a clever lad. so he rings Jaap and says, "Jaap it is your fathers son but not your brother who is it?" Jaap replies, "it is me dave" So dave thanks him and puts the phone down. Next morning David runs over to Alex nad say, "i have got the answer to that question boss, it is Jaap!" Alex frowns and retorts, "NO you stupid fool, it is Dennis Bergkamp!!!"