BRUSSELS -  Belgium's King Albert has abdicated after a 20-year reign with his son Philippe ready to take the oath as the nation's seventh king later in the day.

At the royal palace on Sunday, the 79-year-old Albert signed away his rights as the kingdom's largely ceremonial ruler in the presence of Prime Minister Elio Di Rupo, who holds the political power in this 183-year-old parliamentary democracy.

Less than two hours later, Belgium will get a new king when Philippe, 53, takes the oath before the nation's legislators at the parliament building a short walk across the Royal Park in the heart of the city.

Early in the day, both Albert and Philippe mingled with the crowds under a royal blue sky following a Catholic ceremony that set off the festivities.

Belgium's (front row, L-R) Queen Paola and King Albert II stand with Crown Prince Philippe and Crown Princess Mathilde at a Te Deum mass celebrating the 20th anniversary of the reign of Belgium's King Albert II, the Belgian National Day, King Albert's abdication and the inauguration of his successor King Philippe, at St Gudule Cathedral in Brussels July 21, 2013. [Photo/Agencies]