How could anyone not adore Sophia Loren? The world was in love with her in 1960 and yet Heston was not impressed by her beauty or her talent. She had set Hollywood alight since she signed her original Paramount five-picture deal in 1956. Starring roles opposite Cary Grant, Clark Gable and Sinatra followed in films like It Happened In Naples, Houseboat, The Pride and the Passion, and The Millionairess with Peter Sellers. She was as skilled at drama as comedy with a powerful physical presence and would win the first-ever acting Oscar for a film not in the English language for Two Women (La Ciociara) the year after El Cid. So what went wrong with Heston?

Heston also came into the film a major star and an Oscar-winner in 1959 for Ben-Hur. The director’s first choice for the title and central role, he clearly felt a sense of ownership over his involvement with El Cid. He had enough power that he responded to early drafts of the script that they were “ranging from minimally OK to crappy.”

But then Loren was brought on board. Equally famous, equally acclaimed – and equally strong-willed and opinionated. She wanted the script rewritten with more romantic scenes for her character, Doña Ximena. She would only agree to film for 8-10 weeks so the shooting schedule had to be rearranged to suit her. And she demanded a huge payday.

Some reports have claimed that Loren was paid an enormous $1million for the role, but that didn’t happen until 1964’s The Fall of the Roman Empire. It seems more likely she was paid $200,000, still a huge amount in those days ($1.9million today). And it is claimed more than Heston received.

Loren also negotiated $200 a week for her personal hairdresser, brought in her own screenwriter and had the script translated into Italian and then back into an English she was more comfortable with.

Her co-star was not happy and did not try to hide it. In fact, he demanded that a stand-in was hired to take his place in any close-up scenes that only showed Loren’s face. As the situation deteriorated, director Antony Mann struggled to get the alpha male actor to look at Loren at all.

Charlton Heston: Hollywoodd’s Last Icon by Marc Eliot recounts that Loren’s diva antics “really got him angry,” according to producer Peter Snell.

So much so that Heston was “most uncomfortable” during any love scenes and would, in future, turn down roles that might involve them sharing the screen again.

Mann shot take after take but Heston could barely bear to glance at Loren during passionate scenes and even in the climactic deathbed scene. He would later insist that he was “looking into the future”, rather than into the eyes of his wife.

It was picked up by subsequent reviews, with one saying that “Miss Loren and Heston spend most of the picture simply glaring at each other.”

Heston was also vocally unhappy with the fact that he dramatically aged throughout the movie while his glamorous co-star (with her expensive hairdresser in tow) remained resolutely beautiful.

It reached the point where Heston became enraged by everything the Italian star did. Snell even added that “Loren was one of those actresses who got under his skin with her chronic lateness.”

Heston’s son Fraser also later revealed his father’s anger that Loren insisted that her part was made larger, something that was already happening after positive reactions to her early scenes.

Yet, it was Loren who caused the greatest drama of all when she sued producer Samuel Bronston for breach of contract in New York Supreme Court when the film was released. In the battle of egos, the Italian would strike the final blow – over a billboard.

Variety reported at the time: “On a 600-square-foot billboard facing south over Manhattan’s Times Square, Sophia Loren’s name appears in illuminated letters that could be read from an incoming liner, but-Mamma mia!-that name is below Charlton Heston’s. In the language of the complaint: ‘If the defendants are permitted to place deponent’s name below that of ‘Heston, then it will appear that deponent’s status is considered to be inferior to that of Charlton Heston… It is impossible to determine or even to estimate the extent of the damages which the plaintiff will suffer.'”

Despite all the dramas, the movie ended up grossing a healthy $26.6million on a $7million budget and is still remembered today, perhaps for its impressive scale more than anything else.

Heston later admitted he wished he had been kinder to Loren on-set and they were often pictured together, including at the Hollywood Walk of Fame Star Ceremony to honour her on February 1, 1994.