 Her third sister Princess Christina was born in 1947.On 6 September 1948, her mother succeeded her grandmother Wilhelmina as Queen of the Netherlands, and Beatrix became the heir presumptive to the Dutch throne at the age of ten.In April 1950, Princess Beatrix entered the Incrementum, a part of Baarnsch Lyceum, where, in 1956, she passed her school graduation examinations in the subjects of arts and classics.