LONDON -- With the two simple words "I will," Prince William and Kate Middleton are ending months of buildup and sealing their love with the most public of spectacles, a wedding ceremony at Westminster Abbey that holds the promise of a royal renaissance.

A third of the planet was expected to watch Friday as the future king and queen of England start their lives as husband and wife.

All the clamoring about seemingly every detail -- the wedding dress, her hair, her makeup, the romantic kiss on the Buckingham Palace balcony, the honeymoon -- finally will be answered.

Save perhaps for the biggest question of all: Is this one royal couple who will live happily ever after?

Will their union endure like that of Queen Elizabeth II and Prince Philip, now in its 64th year, or crumble like that of Prince Charles and Lady Diana?

Recent history augurs badly: The first marriages of three of the queen's four children ended in divorce.

But the couple's chemistry brings confidence that this one will work.

William and Kate look fantastic together, seeming to glow with happiness in each other's company, and unlike Charles and Diana they've had eight years to figure out they're made for each other.

But the fate of their marriage will depend on private matters impossible for the public to gauge amid the hoopla. A beautiful bridal gown and eye-popping sapphire and diamond engagement ring do not guarantee a happy ending. Money, power, beauty -- it can all go wrong if not carefully nurtured.

Much will depend on whether 28-year-old William and 29-year-old Kate can summon the things every couple needs to make a marriage work: patience, love, wit and wisdom. But they face pressures most of us don't: the twin burdens of fame and scrutiny.

These are the thorny issues upon which the fate of the monarchy rests, as the remarkable Queen Elizabeth II, now 85, inevitably ages and declines.

Everything is set: The rehearsals have been held, the cakes have been baked, the toast of the best man (William's brother Harry) written, suits and uniforms pressed, hats carefully chosen, shoes buffed, flowers arranged and the champagne put on ice for two exclusive receptions at Buckingham Palace.

Hundreds of street parties are planned as Britons celebrate part of the heritage that makes them unique -- and overseas visitors come to witness traditions they've admired from afar.

"It's part of history," said Norene Shultis of Madison, Wis., who arrived in London Thursday after an overnight flight.

"It's so different from the United States. We don't have royalty. And we think William and Kate will be a good couple and do lots of good things and live happily ever after."

The government has declared a national holiday, universally welcomed by schoolchildren, and there has been a marked proliferation of Union Jacks in the last week as London spruces up for the big event, which has drawn thousands of journalists and tens of thousands of visitors from overseas.

Some 1,900 immaculately dressed guests, including fellow royals from around the world, a smattering of pop stars, sports idols and dignitaries, will jam Westminster Abbey.

A number of famous people were left off the guest list, including President Barack Obama and most other world leaders. Also not invited were Britain's last two prime ministers, Tony Blair and Gordon Brown, in a snub to their Labour Party, which traditionally is not as strong a backer of the monarchy as the ruling Conservatives. The invitation for Syria's ambassador was rescinded Thursday because of Britain's unhappiness with the bloody government crackdown in his country.

The wedding is expected to be watched by 2 billion people across the globe and draw a million well-wishers -- as well as some protesters -- into the historic environs surrounding Buckingham Palace, Westminster Abbey and other London landmarks.

The celebration will be British to the core, from the freshly polished horse-drawn carriages to the sausages and lager served at street parties. Some pubs were opening early, offering beer and English breakfasts -- sausages, beans, toast, fried eggs and bacon -- to wedding fans who wanted to watch it on TV.

The public festivities reflected Britons' continuing fascination with the royal family, which despite its foibles remains a powerful symbol of unity and pride.

Prime Minister David Cameron touched on that theme Thursday.

"It's that mixture of the good-looking prince and the beautiful princess, but it's so much more than that," he said. "It's this institution that's helped bind the country together. And it's got this amazing history that goes way, way back."

But the wedding, like any wedding, is fundamentally about two people. Will their lives together, starting with such high hopes, be blessed by good fortune?

In ways large and small, theirs is a very ordinary romance carried out under extraordinary pressure: Two young people fall in love in college and experience a deep attraction and fondness for each other that ripens over time. They decide to make it official, to become a family, not just lovers who share a home.

Like so many couples, they likely face some doubts as they give up their single status and contemplate starting a family.

It is the most personal, most intimate of decisions, but carried out against a backdrop of intense public interest, simply because William is second in line to the British throne, born to be king.

The royals fervently hope that a joyous union between William and Kate will rub out the squalid memories of Prince Charles and Princess Diana embarrassing each other and the nation with a string of accusations and confessions as their marriage slid toward divorce.

The young couple must sometimes wonder why they cannot simply be left alone to cope with William's demanding and dangerous work as a Royal Air Force helicopter rescue pilot. Instead they are tasked with reviving a monarchy, burnishing a nation's pride, and helping boost public morale at a time of austerity.

Oh, and being happy, too.