In a new book by Spanish author Pilar Eyre is claimed that Princess Diana was just one of the many young ladies King Juan Carlos of Spain pursued in a romantic career in which he is said to have bedded more than 1,500 women.

The explosive claims are made in one of the six volumes about the Spanish royal family written by Pilar Eyre.

Imperious and suave, Juan Carlos looks every inch the old-style monarch with the autocratic manners to go with it. He loves hunting bears, skiing and boating and bedding the opposite sex.

In one picture, King Juan Carlos of Spain sits with the small Prince William, while a radiant Princess Diana, a protective arm round toddler Prince Harry, leans in to share a pleasantry with the good-looking monarch. At the other end of the couch, Prince Charles seems scarcely part of the same holiday party in 1986. He is staring glumly straight ahead like the proverbial gooseberry.

Apparently, it is an open secret in his circles that he is such a keen womanizer that the only woman he does not spend much time with is his wife, Greek-born Queen Sofia.

According to Pilar Eyre, King Juan Carlos, now 74, and Queen Sofia have not shared a bed for 35 years.

In fact, the new book, “The Solitude of the Queen”, says, following an operation on a benign lung tumor at a Barcelona hospital in 2010, the woman who spent most of the time consoling King Juan Carlos during his convalescence was a 25-year-old German interpreter called Corinne.

But can it really be true that our very own Princess Diana was one of Juan Carlos’s most significant conquests? And that it was the relationship between her and the then 48-year-old king, in the prime of his romantic life, that finally put paid to any chance of reviving his marriage?

It is certainly the case that Princess Diana, together with Prince Charles and their young children, holidayed in Majorca with the Spanish royal family several times during the 80’s.

Prince Charles never felt at ease on the sunshine island and much preferred visiting the Duke of Wellington’s estate near Granada on the mainland where the shooting was good.

In one picture, King Juan Carlos of Spain sits with the small Prince William, while a radiant Princess Diana, a protective arm round toddler Prince Harry, leans in to share a pleasantry with the good-looking monarch

But Diana, who loved lounging about on yachts in stylish bathing suits, was right at home on the shores of the Mediterranean where she could show off her figure. And King Juan Carlos, who appreciated displays of female beauty, seems to have acted on an impulse to get closer to her.

After her first trip to Majorca in 1986, Pilar Eyre alleges Diana told her bodyguard Ken Wharfe that Juan Carlos fancied her. Apparently, the king made all sorts of excuses to get tactile with her and used to love bending down with her and inviting her to stroke his old German shepherd dog, Archie.

Another royal biographer, Lady Colin Campbell, has long insisted that Princess Diana and King Juan Carlos embarked on an affair while on a cruise with their spouses in August 1986, and that they took up with each other again the following summer.

“Diana did it to make Charles jealous, but it didn’t work,” says Lady Colin. “Charles couldn’t have cared less.”

According to Pilar Eyre, rumors of the affair intensified later over the curious case of some photos of Diana in a state of undress. These were touted around the world’s publications, only to be taken off the market when someone in Spain paid $45,000 for them. That someone is rumored to have been Juan Carlos, who wanted to protect the Princess’s reputation.

But why rake all this up now? Diana is long since dead, while Juan Carlos, though he retains an eye for a pretty woman, has made it quite plain that he would never divorce his wife, with whom he has three children and eight grandchildren.

Pilar Eyre says she has revealed it for Queen Sofia’s sake.

“In a macho country like Spain, the king’s womanizing image makes him very popular,” Pilar Eyre says.

“Even the women don’t reproach him. On the contrary, they love him because he has such a seductive manner with them. But they don’t feel the same about poor Queen Sofia.

“She is seen as a cold, aloof foreigner. I wanted to show what she has had to put up with.”

Pilar Eyre says she tried hard to find out whether the Queen might also have had lovers in her time, but could come up with nothing.

Though as a young woman she had caught the eye of the Duke of Kent – first cousin to Queen Elizabeth – the Duke then fell in love with the Englishwoman he married, Kathleen Worsley.

Sofia dutifully entered into an arranged marriage in 1962, having met the highly eligible Juan Carlos on a cruise specially convened to introduce Europe’s young royals to each other.

By 1968, they had two daughters and Crown Prince Felipe. But though Sofia had fallen deeply in love with her husband, Pilar Eyre says Juan Carlos was still playing the field.

And by 1975, when he finally came to the Spanish throne after the death of the dictator General Franco, the new Queen was nursing a great sadness. For by then the royal couple was more or less estranged as a result of the king’s persistent womanizing.

According to the book, one of Sofia’s greatest humiliations happened a couple of months after Juan Carlos became king. All of a sudden he sent for a new barber and underwent such a transformation Sofia was convinced he was sprucing himself up for a lover.

A few days later the king packed his suitcase and said he was going hunting near Toledo.

“It’s an all-male outing; you’d be bored,” the king told his wife. Unwisely, Queen Sofia decided to surprise him by arriving at the estate in the middle of the night with their children, the eldest of whom was 12.

Queen Sofia burst through the door, brushed past the servants and, taking the stairs two at a time, discovered her husband in flagrante with an unknown woman. But even being caught by his entire family did not encourage the king to mend his ways.

Pilar Eyre says that throughout her reign, Queen Sofia has consequently been forced to content herself with a life of duty in Madrid, leavened by shopping trips with her daughters and occasional visits to England to visit her brother Constantine, the ex-King of Greece, who has lived in London since he was booted off the throne in 1973.

Lately Queen Sofia has taken solace in religion. She goes to Roman Catholic Mass every Sunday in the palace and attends Madrid’s Greek Orthodox church as well. Her devotions seem to annoy Juan Carlos even more.

King Juan Carlos raised his voice to his mother-in-law, Queen Federica of Greece, when he heard her telling her daughter how the Virgin Mary had appeared before her in a vision in a church near Madrid.

“There was an intense light and peace!” said Federica, at which point the king shouted: “Shut up, you! Don’t fill her head with this nonsense, she will believe it all.”

The tragedy is that despite his behavior, Queen Sofia appears to be as captivated by her husband as she was when they married 40 years ago.

At a recent family funeral Queen Sofia was seen holding tight to him and sobbing on his shoulder as if they were still the closest of companions.

Whether the book will rehabilitate Sofia in the eyes of the Spaniards or merely add to the prestige of Juan Carlos remains to be seen.