In his first speech as king shortly after his father King Albert II abdicated, Philippe made no attempt to paper over those cracks, instead casting the country's division between its 6 million Dutch-speaking Flemings and 4.5 million Francophones as one of its strengths.
"The wealth of our nation and our institutions consists in turning our diversity into a strength," he said after taking his oath of office at the country's parliament.
The ceremony capped a day of transition which started when Philippe's father, the 79-year-old Albert, signed away his rights as the kingdom's largely ceremonial ruler at the royal palace 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, the nation got its seventh king when Philippe, 53, pledged to abide by Belgium's laws and constitution.
While crowds of well-wishers cheered the royal family's every move Sunday, far from everybody in Belgium was happy with the new king.
One Flemish separatist group, the Flemish Interest party, boycotted the parliamentary ceremony, while the legislature's biggest party, the N-VA New Flemish Alliance, sent only a limited delegation.
''We are full-blooded democrats and the purest form of democracy is the republic," said Jan Jambon, the parliamentary leader of the alliance, which has surged to become the main opposition party seeking Flemish independence through democratic transition. It wants the new king not to have any role in coalition negotiations to form a new government, not be head of the armed forces and not sign any laws.
The small N-VA delegation highlighted one of the biggest challenges Philippe will face in his reign—how to remain relevant as a unitary symbol in a nation ever more drifting apart between the prosperous northern Flemings and the economically struggling southern Francophones.
Briefly, at least, the differences took a back seat Sunday as the new royal couple appeared on the palace's balcony cheered by some 10,000 well-wishers braving the relentless sun and 30C (86F) heat.
Flanked by huge bouquets of white roses, lilies and gerbera, King Philippe kissed new Queen Mathilde's hand and got a peck on the cheek in return.
President Barack Obama sent the new king congratulations.
"The president also sends his heartfelt appreciation to King Albert II for his warmth, service, and leadership as he steps down after nearly 20 years," the U.S. government statement said. "Belgium is a valued friend of the United States, and the president looks forward to continuing to deepen this bond in the years to come."
Unlike a disturbance during the oath-taking by King Albert II 20 years ago, when one legislator shouted ''Long live the European Republic," Sunday's ceremony in the packed legislature went off without a hitch, with Albert and Philippe's wife, Queen Mathilde, looking on as he confidently took the oath.
Philippe has long been contested as a worthy successor of Albert, but after years of wooden and timid public performances, the silver-haired, bespectacled monarch came over as poised on the day he had been groomed for all of his adult life.
''Belgium is modernizing itself and it gives me joy," Albert said as he signed away his rights as the kingdom's largely ceremonial ruler at the royal palace.
Albert announced his abdication plans less than three weeks ago, so there was little time to turn the occasion into a huge international event. No foreign royals were at the ceremony. Since the royal transition coincides with Belgium's national day celebrations, a military parade had already been planned.
Philippe will face a tough task in the coming months. The nation holds parliamentary elections in June 2014 amid calls, led by the N-VA, for even more autonomy for the language groups. And perhaps even less power for the king himself.
Up to now, the monarch is still involved in government formation talks by picking go-betweens and brokers to set up multiparty coalitions reaching across the linguistic divide.
Anti-royalists consider even that too much power. ''There is only one place where he belongs and that's in fairytales," said Michel Mischeenaker, an anti-royalist activist who stood outside the church where Sunday's ceremonies started.
After the last elections in 2010, it took a record 541 days to form a government amid bickering about how much more power should be sapped from the central state to profit the separate language groups.
Unlike his five predecessors, Albert tried to avoid politics as much as possible and Philippe is expected to do likewise.
Philippe has prepared for the monarchy as a leader of foreign trade delegations over the past two decades.
''He is a very wise person, a person who is very well prepared," said EU Commission President Jose Manuel Barroso, who attended the ceremony. ''He knows the politics of Belgium and Europe very well."