The second in line to the throne and his long-term girlfriend will marry next spring or summer, but they haven’t announced a date — some say May is likely, others August — or a venue.

Westminster Abbey or St. Paul’s Cathedral, where William’s parents Prince Charles and Princess Diana married in 1981, are considered the front-runners.

A royal spokesman said the couple would be closely involved in organizing all the details.

"It’s very much their day like any other couple, and they will make the decisions all the way through — they want the day to be enjoyable for everybody," he said, speaking anonymously in line with palace policy.

Palace officials said only that the wedding would be held in London. It was too early to estimate its cost or how much the taxpayer will have to stump up — a touchy issue at a time of widespread budget cuts and austerity measures across Britain.

"I don’t think it’s going to be as big, because of constraints, financial constraints, around the country now. I don’t think the royal family will want to be seen, you know, having a big lavish wedding," said Brenda Taylor, a 71-year-old retiree.

The spokesman for William’s office said "the couple are mindful of the current economic situation." He stressed the wedding would not be a state occasion — unlike the wedding for Charles and Diana — because William is not the sovereign or the heir to the throne.

"However, given his seniority, you can expect formal or ceremonial elements," he said.

Funds will likely come out of the Civil List — money provided by Parliament to meet official royal expenses, the queen’s household allowance, or drawn from her personal wealth. That is, unless Parliament votes to give the royal couple extra money for the wedding.

Taxpayers will, at the least, have to pay for security, which will require large numbers of police.

The biggest fashion decision Middleton faces will be her wedding dress.

Deborah Joseph, editor of Brides Magazine, said Middleton will face substantial pressure to choose an English designer, and Hilary Alexander, fashion director of The Telegraph newspaper, expects the princess-to-be to come up with a surprising choice.

"It’s a British royal wedding, there’s no need to look abroad," said Joseph. "She may give a nod to Princess Diana, and use one of her designers, like Bruce Oldfield or Amanda Wakeley, or she may make a statement of her own."

Joseph said Middleton’s decision could define bridal wear for the next decade, much as Diana’s 1981 outfit became the most-copied wedding dress in history.

One easy bet, however: Middleton is likely to use much softer fabric, like tulle or organza, than the stiff taffeta Diana used.

Tuesday’s long-anticipated announcement by the couple was a gift for the British media and government, weary of economic uncertainty and austerity.

Prime Minister David Cameron led lawmakers in the House of Commons on Wednesday in congratulating the couple on their "wonderful news."

"We look forward to the wedding itself with excitement and anticipation," Cameron said.

As commentators dredged up memories of the dazzling nuptials of Charles and Diana, newspapers splashed pictures of Kate and William across their front pages. "The New Romantics," said The Times of London, while several papers noted that William had given his betrothed his mother’s engagement ring. "With Mummy’s ring I thee wed," said The Sun.

Younger brother Prince Harry said he was "delighted that my brother has popped the question!" — and adding that Kate was the sister he had always wanted.

"We’re massively excited," William said in a televised interview that marked the first time the couple has spoken publicly about the tribulations of their love affair, which dates eight years back to their days as university students. "We’re looking forward to spending the rest of our lives together."

William said he had given Kate his mother’s sapphire and diamond engagement ring as a way of making Diana part of his special day.

"I thought it was quite nice because obviously she’s not going to be around to share any of the fun and excitement of it all. This was my way of keeping her close to it all," William said.

William, wary of a media he holds partly responsible for his mother’s death in a Paris car crash in 1997, said he had taken his time in proposing to give Kate a sense of what life in the royal family was like.

"I wanted to give her a chance to see in and to back out if she needed to before it all got too much," William said.

Middleton acknowledged that being in the royal family was "a daunting prospect."

The interview reminded many of a similar TV appearance by Charles and Diana shortly after they became engaged. At that time, Diana seemed frightened of the limelight and withdrawn; by contrast, Middleton seemed at ease in front of the cameras. She said she wished she had met Diana.

"I would love to have met her. She’s an inspirational woman," Middleton said as William looked on.

The future of the royal family depends to no small degree on the success of their union.

The royal wedding represents a chance for the Windsors to start anew. Middleton brings youth and glamour to a monarchy tarnished by divorce and scandal. The marriage will link Middleton — a wealthy commoner whose parents, self-made millionaires, founded a successful mail-order party supply business after working in the airline industry — with William, scion of one of the richest families in the world.

A strong, stable marriage — one that lasts decades and produces heirs — could go a long way toward undoing the damage from Charles’ and Diana’s ugly squabbling and televised confessions of adultery.

"This is their chance to rejuvenate the dynasty," said Patrick Jephson, former private secretary to Diana. "This is an opportunity for a welcome national celebration."

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Gregory Katz, Sylvia Hui and Alia Gilbert in London contributed to this report.