His father, Sir William McMahon, was once prime minister of Australia. But his mother, Lady Sonia got all the headlines for a too-revealing dress at a Nixon White House function.
Look at his father: short, bald, kinda ugly. Look at his mother: younger, leggy, gorgeous, taller than her husband. Sounds like he was either rich (not always the case for Australian politicians) or had other virtues he might have passed on to his son.
We may never know.