Forbes revealed in its 2016 ranking of the richest people on earth that the Norwegian heiress, 19, is now worth $1.2 billion (£862 million). In 2007 her father, Johan Andresen, transferred to her 42% of the stock in Ferd, the family's centuries-old private-investment company.
He also transferred a 42% stake in the company to her sister, Katharina, who at 20 is the second-youngest billionaire in the world. She's also worth $1.2 billion.
Alexandra was only recently confirmed as the world's youngest billionaire because the Norwegian government publishes the tax returns of people over 17.
But despite her affluent upbringing in one of the best-known Norwegian families, she isn't just any rich kid. Alexandra is already an accomplished horse rider, winning several massive competitions in dressage.
Her parents also taught her to be humble and to save. So even though she is worth over a billion dollars, she actually saved her pocket money during her younger years and drove only secondhand cars.
(image source: Alexandra Andresen, modelling for Kingsland equestrian group.Kingsland)