The Netherlands' Willem-Alexander became Europe's youngest monarch on Tuesday after his mother, queen Beatrix, abdicated and his country greeted their first king in 120 years with a massive orange-hued party.
Beatrix, 75, shed a tear before signing the act of abdication at the Royal Palace in Amsterdam, witnessed by Willem-Alexander, 46, his Argentine-born Queen Maxima, 41, and members of the government.
A cry went up from the 25,000-strong crowd in the Dam, the main square opposite the palace where the signing was shown on giant screens.
Willem-Alexander, Maxima and Beatrix appeared in front of the crowds on the palace balcony, bedecked with roses and oranges -- the symbol of the royal house -- before heading for the enthronement ceremony in the neighbouring Nieuwe Kerk.
Beatrix accompanied the king and queen's three daughters to the church, including their eldest, now Princess of Orange Catharina-Amalia, nine.
The Dutch monarch is sworn in before a joint session of the houses of parliament in the deconsecrated church, rather than crowned, because church and royalty are separated in The Netherlands.
Before taking his oath, the king thanked his "dear mother" for the "many beautiful years during which she was our queen".
"I'm treading in your footsteps. I have a clear vision of my office. But no one knows what the future brings," he said.
"Wherever that path leads and however far it goes, I will carry your wisdom and warmth with me," he said.
Dutch animal rights activists have criticised his ermine-lined cloak, but Willem-Alexander noted that it is old and so no blood had recently been shed for it.
MPs and senators then swore an oath to the king, although 16 MPs have refused to do so, saying their allegiance is to the constitution.
A who's who of royals-in-waiting, including Britain's Prince Charles, Spain's Prince Felipe and Japan's Prince Naruhito and his wife, Crown Princess Masako, attended the ceremony.
Princess Masako is on her first trip abroad in nearly seven years, while Prince Charles also attended Beatrix's enthronement in 1980.
-- 'A page in our collective history is turning' --
Police escorted two republicans from outside the royal palace shortly before the abdication after they brandished a large sign reading: "I'm not a subject."
Willem-Alexander is the first Dutch king since 1890 and the first of a new wave of relatively youthful European monarchs.
"Beatrix has been queen for 33 years, our queen," Ruud, 49, told AFP on the Dam after the abdication, a tear in his eye.
"She was a stabilising factor and a symbol of our country. It's sad to see her go after all these years. A page in our collective history is turning."
Amsterdam's population is estimated to have doubled with around a million visitors flooding the city's streets and canals to mark the abdication and enthronement.
Although the monarchy is popular in The Netherlands, some question the cost of the royal household and republicans are seeking a reduction to the king's tax-free salary of 825,000 euros (about $1.0 million).
While Beatrix was known for her formal court, Willem-Alexander has already said that he will not be a "protocol fetishist".
Beatrix's enthronement in 1980 was marred by violent protests and running street battles over a housing crisis that left the city looking like a war zone.
Anti-royalists this time have been allotted six locations in Amsterdam to stage protests. But only around 100 republicans turned up for a protest at just one of the locations, an AFP correspondent reported.
Preparations for the day have been overshadowed by a rancorous debate about the event's official song, known as the Koningslied, which many consider inappropriate, with its mix of traditional and rap music.
A star-studded rendition of the Koningslied was broadcast live from Rotterdam and watched by the royal family on the banks of the Ij river, behind Amsterdam's train station, just before sunset.
The royal couple's three daughters appeared to enjoy the song, but ordinary spectators were uninspired as the lyrics unfurled on giant screens.
"People didn't have enough time to learn the song, especially with all the controversy. Some of them singing live were out of tune, that's a shame," said Yvette, 52.
"At least the chorus is pretty good," added Ria Jongejan, 62, waving a Dutch flag and humming along.
The royal family then took part in a water pageant on the Ij river, accompanied by a flotilla of 250 boats, with Dutch sports, music and ballet stars performing as they sailed by.
Maxima is largely responsible for having made her husband popular after an allegedly boozy youth which earned him the nickname "Prince Pils".
Ever smiling, she has mastered the Dutch language and even taken a charity swim in Amsterdam's canals, endearing herself further in a country that expects its royals to be at once normal and regal.