The letter was written by Esther Hart on the afternoon of Sunday, April 14, 1912.
A few hours later, Titanic brushed the side of an iceberg, punching holes in the ship’s hull that led to her sinking.
In the letter to her mother Hart talked about being sick and not eating the day before. She then goes on to assure her mom, she was feeling better and had gone to church on that Sunday morning.
Esther’s husband Benjamin was supposed to mail the letter but never did.
Instead, the letter was found in the jacket he put on his wife and daughter the night he put them on a lifeboat.
Esther and Eva were among the survivors rescued by the Carpathia the next day. Benjamin was not as lucky.
Auction house Henry Aldridge & Son told the BBC the letter is "the only known surviving example of its type to have been written on that fateful day, surviving the sinking, and having belonged to such a well-known survivor."
Written on Titanic stationary, the letter carries the White Star Line's flag logo, and the header boasts "On board RMS 'Titanic.’”
The Mirror says the letter will be auctioned April 26 in England and is expected to bring between $150,000-$200,000.