For four days, the world waited on word of the tourist submersible and the five people inside who had gone to explore the wreckage of the Titanic. On Thursday, the US Coast Guard announced the tragic news that there were no survivors following a "catastrophic implosion". It wasn't just billionaires aboard: highly respected French explorer Paul-Henri Nargeolet was known as "Mr Titanic" and was part of the early teams that first filmed the wreckage of the ill-fated cruise liner back in 1986.