Queen Beatrix of the Netherlands, the oldest reigning Dutch monarch, announced her abdication on Monday evening in a sudden move three days before her 75th birthday.

After 33 years on the throne following her mother's abdication in 1980, Beatrix said she would relinquish the crown at the end of April, leaving the monarchy to Crown-Prince Willem-Alexander, the oldest of her three sons.

The queen went on national television and radio on Monday evening to announce the departure, having recorded the broadcast earlier in the day. The prime minister, Mark Rutte, delivered a statement on television shortly afterwards, with both stressing that the crown prince had been intensively prepared for the role of monarch.

"The queen was there for us in good times, but also in bad times. Her knowledge and compassion made her an icon of the Netherlands," Rutte said in his statement.

The popular 74-year-old has kept a relatively low profile, aspiring to an image of homely normality by, for example, riding her bike in The Hague. She is also said to be a member of the Bilderberg Group and is ranked among Europe's wealthiest royals.

But behind the scenes, Beatrix took an intense interest in national politics. Although a constitutional monarch, the queen is officially a member of the Dutch cabinet and until last year she had the right of initiative in proposing who should try to form a government in the complex Dutch coalition system.

"Almost 75, [after] 33 years of rule, she's quitting when she's at the top of the world," said a diplomat.

Widowed a decade ago on the death of Prince Claus, a German aristocrat who served as a German diplomat, Beatrix has been visited by intense family misfortune over the past year. Her second son, Friso, was badly injured in a skiing accident in Austria last February and has been in a coma in a London clinic ever since. His wife, Princess Mabel, a commoner prominent in NGO circles in the 1990s in the Balkans, lives in London with their two daughters.

The abdication secures the Dutch throne for Crown-Prince Willem-Alexander at the age of 45. His wife, Princess Maxima, is Argentinian and her family have been involved in court controversies over the past 18 months stemming from her father's role as a civilian minister for agriculture in the Argentinian junta between 1976 and 1981.

Relatives of one of the thousands of "disappeared" killed under the junta sought to mount a criminal case in the Dutch courts 18 months ago. Last March the Dutch prosecutor's office ruled there were no grounds for charging the father, Jorge Zorreguieta.

The ascent to the throne of Willem-Alexander means the Netherlands will have its first king in more than a century. Abdication is also in the tradition of the Dutch monarchy. Beatrix's mother, Queen Juliana abdicated in 1980, her mother, Queen Wilhelmina, in 1948.