Is the rain milk? Is that Debbie Reynolds' voice? Gene Kelly's widow busts the myths about Singin' in the Rain

Here are some facts you probably didn't know – and some facts you thought you knew...

RUMOUR: Ink or milk was added to the water to make it visible in the Singin' in the Rain number

"That is absolutely not true," Patricia says, tackling one of the most popular myths about Singin' In The Rain.

"They say they put milk in the water to make it so you could see it, and it's really preposterous. What is was, is really, really terrific cinematography and lighting."

To make the rain visible, the rain was backlit in front of the plate glass windows of the shopfronts – and the crew had to make sure the equipment wasn't reflected in the glass. Gene is also lit from the front as he comes down the street.

RUMOUR: Gene Kelly was very, very ill on set while performing the Singin' in the Rain number

This one is true: Gene had a temperature of about 103F (39.5C).

"You have to remember he's directing, choreographing and starring in the picture, and so it is hard to have any downtime for someone of that magnitude," says Patricia. "Occasionally people would get sick, but you could often shoot around them, or do other segments and things. But with Gene, he's it."

Gene took a couple of days off, but came in to shoot the number. As director, choreographer and star he didn't get much of a rest.

"It was all draped in black tarpaulin, so he would come outside of the tarpaulin into the daylight and just lie in the sunlight and just kind of bake this fever out of him, and go back in and start over again," says Patricia. "They shot the number in a day and a half."

RUMOUR: Heavy smoker Donald O'Connor (Cosmo) was seriously injured while filming Make 'Em Laugh – and then had to film it all over again because of an error with the footage

Untrue: Donald wasn't hurt, and the footage came out perfectly.

Donald (who Gene thought was one of the greatest improvisational comedians of all time) had a fair amount of downtime on set, so he used to mess around and entertain people with the props he found lying around. Gene had his assistants follow Donald around and write down what he did, and then he strung these "bits" together into a solo number for Cosmo.

Patricia reports: "The flip he does, he had sort of lost his confidence at that point. He had done it as a kid in the vaudeville acts, but they brought his brother back in to re-confirm his confidence.

"You'll read that he went to the hospital, you'll read that he had to go to bed for days. It's not true. The production notes always show when someone checks in, when someone checks out, when someone is ill, if a doctor is called. You'll read that there was a lot of blood on the floor - it's not true."

RUMOUR: The "tap" sounds were dubbed by assistants with their feet submerged in buckets of water

"That's another myth," says Patricia. In fact the taps were dubbed, but by Gene himself.

"It was a really difficult process. Gene hated it. He hated having to tap dance in films, because it was gruelling, he had to go in with a head set and watch himself on film and match it, and had a microphone dangling at his feet, and he said it was very hard to make sure he didn't break an ankle."

There was some experimentation with different sounds as Gene and his sound engineer and his assistants tried to recreate the sound of tap dancing in the rain, but in the end they went with a simple solution.

"The sound engineer was a guy named Bill Saracino. I interviewed him after Gene died and he confirmed absolutely that Gene dubbed his own taps," Patricia recalls. "Gene did standard metal taps, and Saracino created a kind of 'squish' sound in the sound engineering."

RUMOUR: Debbie Reynolds' singing voice is not her own

Hold on to your hats because this one is a bit of a mind-bender.

"I think what's interesting in this movie that people don't realise is that it's a story within a story within a story," says Patricia.

The plot of the film hinges (spoiler alert) on the idea that, as "talkies" replace silent films, Debbie Reynold's character Kathy Selden steps in to provide the singing and speaking voice of shrill movie star Lina Lamont (Jean Hagan).

BUT. Actually: "Debbie Reynolds, when she's dubbing for Jean Hagan, that's actually a woman named Betty Noyes singing, so Debbie Reynolds - when she's supposedly dubbing for somebody else - is actually somebody else dubbing for Debbie Reynolds."

And to make matters even weirder, "When she's dubbing Jean Hagan's speaking voice, when she says, 'Until the stars turn cold', that's actually Jean Hagan's real speaking voice."

RUMOUR: The Singin' in the Rain number had to be re-shot the following day because there wasn't enough water pressure the first time around

"One of the true things is that people came home from work and started using the water in Culver City [California], and they had rigging that was hanging for the water, and they had to suspend the shooting and then hang more rigging," Patricia says.

"It wasn't so much doing it over, they just had to stop and then bring in more and do it again and start the next day."

RUMOUR: Don and Lina's silent movie The Royal Rascals re-uses footage from Gene's 1948 movie The Three Musketeers

The story goes, footage was borrowed from Gene's earlier film The Three Musketeers and stripped of sound and colour to create a silent movie. "Most people now do think it was taken out of the Three Musketeers," says Patricia.

But while the sequence is a little nod to Gene's earlier work, it's all new footage. "If you watch, the costumes are slightly different," she adds.

RUMOUR: Cyd Charisse wasn't originally meant to be in Broadway Melody

True. The Broadway Melody sequence was originally supposed to feature Donald O'Connor, but he had another engagement. "They needed someone - a real dancer - to be able to pull that off. And so they brought Cyd Charisse in," explains Patricia.

"She had recently had a baby, which is remarkable. She had never danced jazz. She was a classically trained ballerina, and so Gene had to - he said it was very, very hard to get her off pointe and to dance jazz, but she's magnificent.

"That costume, the censors would come in and they would measure the lengths of the skirts and the décolletage, and everything was monitored and then Gene would slit things! He called it cheating the censors."

RUMOUR: The more risqué scenes in Broadway Melody were censored

Talking of censors, rumour has it that part of the Broadway Melody sequence was cut. This is certainly true in several countries, including Spain.

"The scarf dance was cut out of the picture in several countries because they found it too risqué." Patricia reveals.

"They figured it out, it's love-making. And in the most beautiful way. Isn't that amazing?"

RUMOUR: The character of RF Simpson was based on producer Arthur Freed

Studio boss RF Simpson was pretty close to Singin' In The Rain producer Arthur Freed.

Patricia says: "There are all these little references to things. Arthur Freed, the producer – Judy Garland referred to him as the Tank, he would come on and he would be kind of awkward, kind of clumsy on the set. When he pulls the wire – that's a reference."

Singin' in the Rain airs at 4.10pm on Channel 5 on Christmas Day