Sir David Attenborough is celebrating his 99th birthday today (May 8) with no signs of slowing down.

He marks the occasion by launching Ocean, a new documentary underscoring the critical role of our planet's seas in maintaining a healthy ecosystem.

Yet, despite his focus on Earth's wellbeing, Sir David has about his own health. In a candid 2021 conversation with US journalist Anderson Cooper, he shared his deepest fears regarding ageing and mortality.

When asked by the 60 Minutes presenter: "What are you most fearful of at this moment?", Sir David admitted his dread of "becoming helpless and gaga," particularly in the face of diseases such as .

As he nears the milestone of 100 years, questions about his mortality have become more frequent.

During a 2019 interview with the Australian broadcaster ABC, he reflected on his thoughts about passing away, expressing: "I just hope it won't be painful - and I hope it won't be tiresome for others."

Sir David's legacy extends far beyond his groundbreaking nature documentaries. As a former BBC executive, he was instrumental in commissioning iconic series such as Civilisation, and The Old Grey Whistle Test, while also transforming the broadcaster's approach to covering major sporting events, reports .

He saved from the brink of cancellation in 1965, assuring Football League executives that "nobody watched BBC2" thus allaying fears of impacting match attendances.

Sir David later reflected during a documentary for Match of the Day's 50th anniversary in 2014, admitting his statement was "more or less true," as "BBC2 was only visible in a small part of the country - London and Birmingham - and it had a tiny number of viewers".

In 1969, he played a pivotal role in introducing colour television to the UK, which included bringing snooker broadcasts to life.

He also convinced Wimbledon officials to switch their tennis balls to yellow, enhancing visibility for TV audiences, a change that eventually became the global standard.

Speaking with Anderson Cooper, Sir David reminisced about the moments he'd love to experience anew: "Seeing a coral reef for the first time, watching a hummingbird, sitting alongside a gorilla, and holding my first born baby," he shared.

The esteemed broadcaster is also not without his saddest memories. When asked about the most gut-wrenching moments from his extensive career documenting nature's raw beauty and ferocity, Sir David told the Call of the Wild podcast: "I suppose the most obvious one that I remember particularly vividly, of course, is the first time when I went to a coral reef.

"I thought I was going to dive in, in eastern Australia on the Barrier Reef, and instead of seeing the most marvellous, beautiful, extraordinary, wonderful wonderland, it was a cemetery. It was just white, dead coral. And we were responsible."