Sir David Attenborough's new film is the 'greatest message he's ever told', says its producer. 

Ocean: With David Attenborough will see the legendary environmentalist, 98, delve further than ever before into the 'most important place on earth' - its oceans.

After being significantly damaged by fishing and pollution, the film argues the sea is 'at a crossroads', but 'it can bounce back'. 

Ocean will be released on Sir David's 99th birthday this Thursday, and has been described as a step away from his usual style of film. 

Toby Nowlan, the movie's producer, said: 'This is not about seeing brand new natural history behaviours. 

'This is the greatest message he's ever told.'

The film's premiere will be held tonight with a blue carpet set to be rolled out at London's Royal Festival Hall. 

A host of celebrities are expected to be in attendance including Chris Martin and Coldplay, Benedict Cumberbatch, astronaut Tim Peake, Geri Halliwell-Horner and Simon LeBon.

Never-seen-before graphic footage of the damage that bottom trawling - a common fishing practice around the world - has done to the seabed is said to feature in the film. 

The pictures will display how the chain that trawlers drag behind them scours the seafloor, forcing the creatures it disturbs into the net behind.

The process also releases huge amounts of carbon dioxide into the sea, something which contributes to global warming. 

Sir David will examine inspirational stories of ocean recovery in areas where destructive fishing is banned - such as the Isle of Arran, Scotland and Hawaii.

The broadcasting icon contends that 'the ocean can recover faster than we can ever imagine'.

But 'we are running out of time', says Attenborough, who candidly admitted he may not be around to see our oceans saved as he 'nears the end of his life'.

During the heartbreaking admission in the film's trailer, he said: 'When I first saw the sea as a young boy, it was thought of as a vast wilderness to be tamed and mastered for the benefit of humanity.

'Now, as I approach the end of my life, we know the opposite is true. After living for nearly a hundred years on this planet, I now understand that the most important place on Earth is not on land, but at sea.'

He added: 'Today, it is in such poor health I would find it hard not to lose hope were it not for the most remarkable discovery of all.'

'If we save the sea, we save our world. After a lifetime of filming our planet, I'm sure nothing is more important.'  

Sir David further made a reference to his years on this earth as he opened up about the extraordinary ocean discoveries over the decades and how important it is to preserve the health of the oceans.

He said: 'My lifetime has coincided with the great age of ocean discovery. Over the last hundred years, scientists and explorers have revealed remarkable new species, epic migrations and dazzling, complex ecosystems beyond anything I could have imagined as a young man.

'In this film, we share some of those wonderful discoveries, uncover why our ocean is in such poor health, and, perhaps most importantly, show how it can be restored to health. This could be the moment of change.

'Nearly every country on Earth has just agreed, on paper, to achieve this bare minimum and protect a third of the ocean.

'Together, we now face the challenge of making it happen.' 

The Discovery+ series also features historical footage, including scenes from back in 1957 when the animal lover first attempted scuba diving on the Great Barrier Reef.

The much loved TV personality has been on screens for over 70 years, with his first appearance being back in 1954, having started at the BBC in 1952. 

He was brought in to front wildlife series Zoo Quest after the intended presenter fell ill on location. The series, which was broadcast until 1963, took British viewers into far-flung countries - and supercharged the young naturalist's career. 

His groundbreaking Life On Earth series, which began in 1979, really put him on the map.

In the decades since, Sir David has been behind some of the most successful documentary series in British television, including The Living Planet, Planet Earth and Frozen Planet.

His work has inspired dozens of other TV presenters.

As well as his passion for work, David's other big love was his wife Jane Oriel, whom he was married to for 47 years.

The couple shared two children, son Robert and daughter Susan, who are now both in their 50s. 

Jane from a brain haemorrhage in 1997 aged 70.   

When she slipped into a coma, he was in New Zealand making The Life Of Birds yet managed to get to her bedside before she died.

In his memoir, Life On Air, David recalled the moment Jane passed away, noting how 'lost' he felt at that point.

He shared: 'She did and gave my hand a squeeze. the focus of my life, the anchor had gone…now I was lost.

In a 2017 interview with The Guardian, the naturalist praised his wife as he opened up about his regrets at being away from his family for long stretches of time while filming all over the world.

He shared: 'I was away for three months at a time. If you have a child of six or eight and you miss three months of his or her life, it's irreplaceable; you miss something. And I did. My dear wife was very understanding about it.'