British author Louise Patten says the accepted account of the cause of the Titanic disaster, an unavoidable collision with an iceberg on 14 April 1912, is a fabrication.
She says her grandfather, Second Officer Charles Lightoller, hid the truth - that there was time to avoid the iceberg - but the ship turned the wrong way.
Ms Patten has revealed the truth in a novel, Good as Gold.
She says confusion about steering orders was responsible for the liner sinking in the Atlantic Ocean on its maiden voyage with the loss of 1500 lives.
Ms Patten says an officer steered into an iceberg instead of away.
She said the tragedy had occurred during a period when shipping communications were in transition from sail to steam.
Two different systems were in operation at the time, Rudder Orders (used for steam ships) and Tiller Orders (used for sailing ships).
Crucially, Ms Patten said, the two steering systems were the complete opposite of one another, so a command to turn 'hard a-starboard' meant turn the wheel right under one system and left under the other.
She said when the helmsman, who had been trained in sail, received the direction, he turned the vessel towards the iceberg with tragic results.
The BBC reports Ms Patten has worked the story of the catastrophe into her novel.
While Second Officer Lightoller was not on watch at the time of the collision, his granddaughter says a dramatic meeting of the four senior officers took place in the first officer's cabin shortly before Titanic went down.
While there, Lightoller learned about the fatal mistake.
But she claimed what followed was a deliberate decision. White Star Line chairman Bruce Ismay persuaded Captain E.J. Smith to continue sailing.
The truth of what happened on that historic night was deliberately buried, she said.
Ms Patten's grandfather decided not to disclose what he knew and even kept his story from an official inquiry into the sinking.
By his code of honour, he felt it was his duty to protect his employer - White Star Line - and its employees, Ms Patten said.
It was made clear to him by those at the top that, if the company were found to be negligent, it would be bankrupted and every job would be lost.
The inquiry had to be a whitewash. The only person he told the full story to was his beloved wife Sylvia, my grandmother.
The wreckage of the Titanic was discovered in 1985, 4km beneath the surface of the sea.