New York | Just as last week's cheating scandal begins to fade from our collective memory, another KarJenner bombshell hits: Kylie Jenner, the youngest of the clan, has become the youngest billionaire in the world.

Forbes magazine declared as much in its annual billionaires list, published on Tuesday (Wednesday AEDT). Having accumulated an estimated $US1 billion ($1.4 billion) by age 21, her entry states, Jenner is "the youngest self-made billionaire, reaching a 10-figure fortune at a younger age than even Mark Zuckerberg (who was 23 when he hit that mark)."