If His Serene Highness Prince Rainier of Monaco is not so serene lately, there’s good reason for his choler to rise and his lips to quiver. Sources say he is unnerved, upset and undone over “Grace,” Robert Lacey’s brand new biography of Princess Grace which, among other sweet anecdotes, reveals her predilections for young men, surrounding herself with them during her middle years when Rainier was said to have been indifferent to her, at best.

Sources also say that Rainier, in his anguish, a more or less permanent state for him what with his cute children and all, called upon Italy’s Prime Minister Silvio Berlusconi for advice, asking that worthy one what means he could take to defend himself and his late wife from the book’s charges. Rainier made it clear that he knew all about Grace and her young men, that they were with her to work on her artistic projects, that she used them as escorts when he was too busy working to accompany her to every lighted candle.

Berlusconi is said to have replied that the best tack to take was to go on television and do an interview refuting many of the stories in the book. But Rainier decided not to do it. The thought of going through that ordeal, maybe opening up more doors that should remain closed, was more than he could bear. Berlusconi then suggested Princess Caroline might want to take to the tube, but Caroline, though terribly disturbed herself over the book, also refused, feeling that it was daddy’s call. The moral of this story, friends, is: If you are famous, plan not to die.

The Johnson & Johnson heiress, Elizabeth Ross Johnson, called Libet on the New York social and philanthropic scene that is her habitat, and her husband of four years, Christopher Kennan, son of the revered elder statesman George Kennan, have decided the only way to go is by different routes. They have separated, and a divorce is in the offing, but all is friendly and fine with mutual regard and respect on both sides. It’s just — well, what do you do when the magic is gone? Libet doesn’t hang around.

Is this sort of thing catching? Fernanda and Frank Gilligan’s marriage has also hit that well-known rocky road. They, too, are well-known on the social scene. Fernanda’s father is Ambassador Francis Kellogg, and her former stepmother is none other than Mrs. Sid Richardson (Mercedes) Bass of New York, Fort Worth, Aspen and whatever’s left.

Barry Kieselstein Cord, designer of divine jewelry and bags that cost as much as the jewelry, is still on a high after his team of vintage race cars took three blue ribbons at his annual Labor Day Race at Limerock, Conn. He had hoped it would happen the night before when he and his stunning wife, CeCe, entertained a bunch of swells from across the globe on the lawn at Foxgate, their 200-year-old farmhouse in Millbrook. Everyone was there — Blaine and Robert Trump with her parents, the Joe Beards; Carolyne Roehm (who gave her own party over the weekend at her Connecticut farm, Weatherstone); Sandy and Bob Pittman, Christopher Kennan (no Libet), CeCe’s brother, Chris Eddy, and his wife Jamie, the Massimo Ferragamos, Libby and Basil Mavroleon and other sterling examples of the surrounding gentry. Plus the guests of honor, race car drivers Gene Felton from Atlanta, Peyton Feltus from Dallas and Seamus Noland from Ireland.

Barry and CeCe’s beautiful young daughter Elisabeth was there with some of her teen friends (they looked nothing like the “Beverly Hills 90210” gang), who all entered the trout-fishing contest while Barry stirred up some of his famous Blue Hurricane Margaritas, guaranteed to heat up the conga line while Joe Cool’s band played and the bonfire roared.

On race day, the Kieselstein Cords’ guests lunched under a tent surrounding the race trailer, and after the big win, they all headed back to Foxgate again for a champagne supper. (It would be nice to report that Team Kieselstein Cord repeated their great win at Watkins Glen this past weekend, but they had to satisfy themselves with one win, one second and one car blowing the hell up).

One of the really fun things that happened at the prerace Foxgate party was when that leggy blonde showed up on the arm of her investment banker-type friend. She was dressed like a Palm Beach Popsicle in a tight pink suit with a very short skirt. After looking around and realizing that Millbrook attire is much more casual, she quickly retreated to her new black Bentley in the parking lot to retrieve some more appropriate attire from the trunk. Then, to the delight of the male guests — and the parking attendants — she proceeded to strip down to her very skimpy white G-string before reappearing in her country gear. Man does not live by race cars alone.

Speaking of that sort of thing, Donna Karan and Donatella Versace, sister of Gianni, gave the spectators quite a show at the Fashion Group’s party honoring Bernadine Morris. Both were wearing dresses so low, one was obliged to hold one’s breath lest something pop out. Both looked very sexy, but if either had worn a Wonderbra some of the guests might have had to move across the street to make room.

Anyhow, the designers who came over from Paris to honor Bernadine, especially, Gianfranco Ferré, Christian Lacroix, his partner Jean-Jacques Picart and Emanuel Ungaro were the quintessence of Gallic charm. And Ungaro’s wife, the adorable Laura, stole the show at every party. She can’t speak a word of English, but she doesn’t have to.

Bernadine was at Annette and Oscar de la Renta’s cocktail party at home before the show, wearing Oscar’s flirty little black feather and silver sequin jacket. “I wouldn’t dare wear anything else here,” said Bernadine. Yes she would. It was almost thrilling to see Annette in brilliant red and Gretchen Grisanti in rich brown among all the black dresses. The news in Paris and here, too, is color, but you have to beat New York women with sticks to get them out of black. That fear of being overdressed or not safely dressed doth make cowards of us all.

Nancy, Lady Keith, known to the social and fashion world as Slim, was sleek, chic and remarkably good-looking in her heyday. She was always so well-turned out and had the sort of flair others envied. She was the sort of woman who would rather die than gild the lily. Slim’s daughter, Kitty Hawks, has retained many of the treasures her mother left, but some of the things her mother collected and used will go on sale at Sotheby’s Arcade on Sept. 20.

You may bid on such as her Japanese gold-mounted black traveling case, her Louis Vuitton luggage, and furniture, silver and porcelain from her houses, in London, New York, Long Island and Beverly Hills. Before the auction, Kitty will give a brunch at Sotheby’s for some of her mother’s closest friends including Lauren Bacall, whom Slim discovered when Bacall was a New York model. Bacall is said to have based her role in the film “To Have and Have Not” on Slim and her wonderful brand of cool.