Mr Golden was on the Polar Prince support ship to give presentations about the Titanic when the submersible went missing.

“When the sub was overdue we weren’t unduly concerned because communications break down a lot in the ocean,” he explained.

“But when the alarm was finally raised, that’s when we realised that there were some serious issues.”

A major search and rescue operation was launched by the US Coast Guard.

A few days in, underwater sounds detected by search aircraft raised hopes that these were coming from the missing sub.

But it’s now known that those onboard most likely died instantly after Titan suffered a catastrophic failure as it neared the Titanic at the bottom of the Atlantic.

“We lived in false hope for four days,” Mr Golden said. “There’s still a lot of questions to be answered.”