NEW BRIDE Madonna, who just gave birth four months ago at age 42, had a wedding day surprise for her guests gathered at a remote Scottish castle: She believes the “magic” castle will help her get pregnant!

That answered the question everybody had been asking: Why get married in a dank, cold castle in a remote corner of Scotland in the winter?

“We conceived Rocco here in Skibo Castle. The place worked like a charm, so we want to try for another baby here,” she told a friend. “At my age I need all the help I can get!”

That’s the untold story behind the superstar’s $3 million “Braveheart”-themed wedding to movie director Guy Ritchie, 32.

Madonna had locals in Dornoch scratching their heads when she rented the entire castle for three weeks. But she explained: “We wanted to make sure we had enough time to make a baby. Too bad I ovulate only once a month!”

Guy is delighted the woman he calls Madge is determined to give their son Rocco a baby brother or sister before he’s much older, sources say. And Madonna’s daughter Lourdes, 4, wants a baby sister now that she has a little brother.

London bookmakers are laying 33-1 odds that Madonna’s marriage will end in divorce within five years.

“Madonna comes from a big family, and Guy’s so overjoyed at being a new dad he’s told her it’s O.K. with him too,” said an insider. “Madonna knows that if she wants to have a bigger family, she can’t wait any longer.”

Said another insider: “Guy is a traditional type and at first he wanted to get married before they had kids. When Madonna got pregnant so fast it was a big surprise to both of them.

“But because of Madonna’s age, she didn’t want the stress of a wedding while she was pregnant in case it jeopardized the baby’s health.

“And she didn’t want to waddle down the aisle like it was some shotgun wedding!

“So they put Rocco’s birth first. Now they can give priority to trying for another baby.”

And there’s good news for Madonna and her new hubby:

Well-known Scottish seer Swein MacDonald says Madonna and Guy will have TWO more children — one of them conceived on their wedding night!

The bearded 70-year-old recluse lives in a tiny cottage just miles from secluded Skibo Castle. The visionary foretold the marriage of Diana and Charles — and their tragic breakup — as well as the birth of Prince William within a year of their wedding.

“Madonna and her man will have two more children,” he said. “They are good people and will enjoy a long and happy marriage. There is a lot of trust and love there.”

Insiders say there’s another touching secret behind Madonna’s wedding at the magical Scottish estate: It’s where Guy asked Madonna to marry him, on bended knee, 12 months ago.

But most of all they’re convinced little Rocco was conceived in the old four-poster bed of Skibo’s magnificent bridal suite — the same bed they retired to once again on their wedding night.

The couple’s top-secret ceremony was witnessed by only 60 close friends and family.

Before the wedding Guy and Madonna, in a Scottish tradition, planted an oak tree near the castle as a symbol of their long-lasting love — and vowed to return each year to see it grow.

The night before the wedding, the couple followed tradition by sleeping in separate bedrooms.

On the big day, the fog and mist-shrouded castle’s ancient Great Hall — scene of the wedding ceremony against the backdrop of a magnificent stained-glass window — was lit by hundreds of candles and decorated with $75,000 worth of red roses and white lilies.

Madonna was given away by her father Tony Ciccone, despite a rift between the two of them that went on for years. Gwyneth Paltrow was her maid of honor. Madonna’s excited daughter Lourdes served as flower girl.

Guy had two best men — movie producer Matthew Vaughn and London club boss Piers Adam.

Madonna told them before the ceremony that they could crack as many jokes as they wanted to in their “best man” speech about Guy — but warned them not to embarrass her by mentioning any of Guy’s old girlfriends.

Guests said Madonna looked radiant in a $30,000 off-white embroidered satin wedding dress specially made by close pal Stella McCartney, Paul’s daughter.

She wore Cartier’s fabulous diamond-encrusted Princess Grace tiara, and on her wrist she proudly wore a $72,000 diamond-encrusted antique French bracelet.

Out of respect for Guy’s Scottish roots, Madonna also wore a tartan sash. And in a nod to her rock image, she wore diamond-studded cowboy boots under the dress.

Guy wore a kilt in the Hunting Mackintosh tartan of his clan — with nothing underneath it.

“When Madonna arrived and walked down the aisle everyone turned and gasped because she looked so amazing,” a pal revealed.

Guests said there wasn’t a dry eye in the hall after Guy joined his bride at the altar and told her quietly: “You look beautiful — I love you.”

Both Madonna and Guy wept as they said the vows they had written.

The fiercely independent singer did break with tradition when she didn’t promise to obey Guy.

Instead she vowed to “cherish, honor, delight in family and always keep and hold to one another.”

Celeb guests watching the ceremony included maid of honor Gwyneth, Sting and his wife Trudie Styler — who introduced Guy to Madonna — fashion designers McCartney, Donatella Versace and Jean Paul Gaultier, and close Madonna pal Rupert Everett.

Minister Susan Brown had the newlyweds and guests smiling at the end of the ceremony when she gifted Madonna and Guy with a pack of two rolls of coarse Scottish toilet paper to symbolize her hope that the marriage should be long and strong.

After the ceremony a piper led the couple and guests into a sumptuous wedding banquet in the Grand Dining Room, where Madonna and her new husband sat at the head table in two oak chairs.

The reception’s decor had a theme from “Braveheart,” the Mel Gibson movie about medieval Scottish hero William Wallace.

Waiters even had their faces painted blue in the style of ancient Scottish warriors.

Guests feasted on starters of langoustines, salmon and mussels, then a choice of haggis, venison, or Aberdeen Angus beef with roast potatoes and red cabbage.

They washed it all down with vintage champagne, Beaujolais Morgan wine and malt whiskies.

The magnificent wedding cake — it had to be carried by four waiters — was in the shape of a grand piano and covered in rich chocolate.

After the reception the newlyweds and guests danced into the wee hours in the castle’s ancient cellars, and a traditional fiddle band had the wedding party dancing wild Scottish reels.

The last time the tiny town of Dornoch, population 2,275, saw such a crowd-pulling event as Madonna’s wedding was in 1727 — when the last Scottish witch was burned at the stake!