King Philippe of Belgium takes the oath during a ceremony at the Belgian Parliament in Brussels, on July 21, 2013. Prince Philippe was sworn in before parliament as Belgium's seventh king on Sunday, the country's national day, after his 79-year-old father Albert II abdicated. (Xinhua/POOL)

Prince Philippe was sworn in before parliament as Belgium's seventh king on Sunday, the country's national day, after his 79-year-old father Albert II abdicated.

Philippe took his oath in Dutch, French and German, the country's three official languages.

"I swear to observe the constitution and the laws of the Belgian people, to preserve national independence and the integrity of the territory," Philippe said shortly after Albert II signed the act of abdication at the royal palace after a 20-year reign.

Philippe, 53, is a fighter pilot and parachutist with degrees from the world's top universities. At the age of 39 in 1999, he married a young Belgian aristocrat 13 years younger than him, Mathilde. They have four children. At age 40, Matilda is the first queen of Belgian origin in the country's history. Their eldest daughter Elisabeth, 12, is now the new Crown Princess.

For a long time, Philippe, as crown prince, led numerous trade missions to promote Belgian exports.

Albert II announced his abdication decision on July 3, citing "age and health" as the reasons for not continuing to carry out his duties. Albert II was sworn in as Belgium's sixth king in 1993, succeeding his brother Baudouin who died at the age of 62, and has become the first Belgian king to voluntarily step down.

During his reign, King Albert II saw several political crises. He played a major role in helping to end a situation where was Belgium without a government for 541 days, a world record, following the early general elections in 2010. The new King Philip will face in 2014 the new general elections, where the Belgian political scene will be re-tested.