It describes scenes of “horror” and “sublime heroism” as passengers tried to escape the sinking vessel.

Miss Icard is believed to have been a maid to a wealthy American passenger called Martha Stone, the widow of the president of Canadian telephone company Bell Cie.

They boarded the Titanic as first class passengers in Southampton as they made their way back to the United States after a long period of travelling.

The pair escaped the sinking passenger ship in a lifeboat and were rescued by the Carpathia before being taken to New York.

It is thought she wrote the letter to the daughter of another woman whose mother also survived the disaster.

The letter, written in blue ink, is addressed to a woman believed to be called Madame Ausein, although the name is slightly unclear and no one of that name appears in the list of survivors.

The letter emerged after a user of the online community Reddit requested help in translating a set of letters written by Miss Icard that he bought at an auction around two years ago.

Although it has yet to be authenticated, if real, it provides a vivid first hand account of the night the Titanic sunk. In the letter, Miss Icard tells how even 43 years after the tragedy on 15 April 1912, she still had nightmares about that night.

She wrote: “Towards eleven o’clock Mrs. Stone and I went to bed. Three quarters of an hour later, as the liner was cruising at full speed, a terrifying shock threw us out of bed.

“We were intending to find out what was happening, when a passing officer told us ‘It is nothing, return to your cabin.’ I answered ‘Listen to that loud noise, it sounds like water is flowing into the ship.’

“Upon our return to the cabin I saw that our [female] neighbour from across the passageway had gone back to bed.

“Her daughter arrived in a panic, yelling ‘Mama, quick quick, get up it’s very serious.’

“I helped Mrs. Stone to dress, she took her lifebelt and told me ‘come quickly. I was trembling, and still in my dressing gown, I took a coat, my lifebelt, and followed her on deck.”

Miss Icard describes how she managed to get her travel blanket and fur coat which she had left on her lounge chair earlier in the day and how they helped protect her from the bitter arctic cold.

She also tells how she narrowly escaped being trapped below deck after trying to go back to her cabin to retrieve her mistress’s jewellery.

She added: “We felt beneath our feet the deck lean towards the depths. I went back belowdecks to retrieve the jewels of Mrs. Stone [but] fortunately, I choose the wrong stairwell and returned to the deck halfway there.

“Fortunately for me, for I would have never come back up again.

“At this moment we witnessed unforgettable scenes where horror mixed with the most sublime heroism. Women, still in evening gowns, some just out of bed, barely clothed, dishevelled, distraught, scrambled for the boats.

“Commander Smith yelled, “Women and children first”. Firm and calm, in the throng, officers and sailors were taking the women and children by the arm and directing them towards the lifeboats.”

She also details heart-rending scenes on board as wives were put aboard lifeboats, leaving their husbands on board to die with the sinking vessel.

Miss Icard wrote: “Near me were two handsome elderly [people], Mr. and Mrs. Straus, proprietors of the great store Macy’s of New York. She refused to go into the boat after having helped in her maid.

“She put her arms around the neck of her husband, telling him: ‘We have been married 50 years, we have never left each other, I want to die with you.’

“Semi-conscious, in a neighbouring boat was put the young wife of the millionaire J. Jacob Astor, returning from their honeymoon voyage she was 20 years old, him 50. She latches on to him, he was obliged to push her away with force.”

She added: “There had been sublime gestures, a stranger undid his safety belt to give it to an old woman who couldn’t find a spot in any boat, and told her ‘You’ll pray for me’.

“The billionaire Benjamin Guggenheim after having helped the rescue of women and children got dressed, a rose at his buttonhole, to die.”

At one point the crew sung a hymn to help lift the passengers spirits before the lifeboats were lowered.

Those lucky enough to be in one of the lifeboats were then asked to row quickly to get clear of the sinking Titanic.

Miss Icard also describes how she discovered a young man hiding in the bottom of the lifeboat where he had stowed away and the horror as the Titanic slipped beneath waves.

She said: “I took the oars and rowed with so much energy that my hands were bleeding and my wrists were paralysed, because we had to hurry to escape the huge chasm that was going to be opened when the Titanic would sink.

“It was at this moment that I noticed that someone was hidden underneath me. I didn’t have the strength to reveal his presence. I’ve never known who the man who saved his own life this way was.

“Suddenly, there was darkness, whole and inscrutable, shouts, horrible yells, rose in the middle of the creaks of the boat, then that was it. Sometimes, 43 years after the tragedy, I still dream about it.”

Miss Icard was one of just 745 people who survived out of 2,229 passengers and crew who were on board the Titanic.

She was eventually rescued by the Carpathia the next day, but perhaps the most vivid image is the serene calm she describes during sunrise the morning after the disaster.

She said: “After that night of terror, at first light, before the arrival of the Carpathia which would collect us dazed, completely exhausted, our boat and some others went back to the scene of the tragedy.

“The waters were calm and bare, and nothing could suggest that the sea giant was engulfed there. Alone, in front of us, two cathedrals of ice which were pinkening under the first sunlight offered a spectacle of rare beauty.”

It is thought that Miss Icard wrote this letter in 1955 from her home in Grenoble after being encouraged by her family to record her memories of the tragedy.

She eventually died in July 1964 and was the longest living French survivor of the disaster.

Her letters were sold at auction around two years ago and the Reddit user claims to have bought them before seeking help to have them translated.

He said: “I’ve had them for close to 2 years now sitting in the same spot as I’ve procrastinated on getting them translated then framed along with her passport.

“I actually bought them at an auction and this is the first time they were ever let go by the family.

“Her family begged her to write the letters before she died or forgot much, reluctantly they put them up for auction and I won the bid.”