A North East university lecturer - who was the first Brit to dive to the Titanic - has paid tribute to one of the victims who died onboard the Titan submarine.
Paul-Henri Nargeolet died along with Stockton Rush, Shahzada Dawood, his son Suleman, Hamish Harding following a "catastrophic failure" close to the wreckage in the North Atlantic.
Sunderland University lecturer Dik Barton, who previously dived the Titanic wreck with f ormer French navy officer Nargeolet, described him as an "extraordinary individual" and "iconic" underwater explorer.
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During an interview with BBC Breakfast, he reminisced about the dives they'd performed together.
He said: "PH was an extraordinary individual. He is an iconic underwater explorer. He is an amazing individual, I worked with him back in the early 90s when we first dived to the wreck.
"But I think what is important to understand is what we were doing was professional underwater exploration, using purpose-built submersibles which were designed to work at those depths."
He added: "Physics is important here because it is hard to crush a ball and the operating system we had was a sphere, a titanium sphere, and the other vessel, the Titan, that was used was basically a tube."
He said this meant there was an issue with design and maintenance, before adding: "Unfortunately, there were many red flags flying here. Then you have to think about is it a good place to go as a tourist?"
Nargeolet was the director of underwater research for E/M Group and RMS Titanic Inc., had completed 37 dives to the wreck and supervised the recovery of 5,000 artefacts, according to his company profile.
RMS Titanic, Inc., the company that owns the salvage rights to the Titanic shipwreck, mourned the long time employee known as "PH."
"The maritime world has lost an iconic and inspirational leader in deep-sea exploration, and we have lost a dear and treasured friend," the company said in a statement Thursday.
Friend and former colleague Matthew Tulloch said Nargeolet loved his work from the time they first collaborated in the 1990s up until Nargeolet's death.
"I never got the impression that he was looking forward to retirement," Tulloch said with a small laugh. "You sort of think of people as they retire, then they can go on and do things that they love to do. This was exactly that for him - I can't think of anything that I'm aware of that he would enjoy doing more than traveling around and sharing information and his experiences with people."
Long time friend and colleague Christian Petron hailed Nargeolet as "surely one of the world's greatest explorers of the deeps."
