Sir David Attenborough thinks his memory is dwindling.

Sir David Attenborough

Sir David Attenborough

The 90-year-old legendary presenter is currently travelling around the globe for filming for 'Blue Planet II' but has admitted he's "run into a few problems" while writing the script for the seven-episode series because of his difficulty to remember names.

David - who turns 91 next month - noticed his memory lapse while he was trying to recall the name of a flower during a recent trip to Jura Mountains in Switzerland.

He told the Daily Telegraph newspaper: "There were these searing yellow fields and I can't think of the damn name. I wanted to say something about it but I couldn't and it wasn't until we got quite close to Geneva that I thought, of course, oil seed rape."

The naturalist will make two appearances in the forthcoming series - the same amount of times he was seen in last year's 'Planet Earth II' - and is convinced that people will be blown away by the footage they've managed to obtain from the shores in Florida.

He said: "I've just come back from Florida where we have been filming spinner sharks. There are 20,000 of them and people don't even know they're there.

"From a helicopter you can see this great column of fish and sharks, and just over there, there are people exercising their dogs on the beach."

Bosses at the BBC announced they were planning to do a second instalment of 'Blue Planet' after 'Planet Earth II' went down such a storm with viewers late last year.

The forthcoming series, which was filmed over four years using new camera technology and techniques, was last on screens six years ago but will return later this year.

The new-and-improved technology used during filming allowed the camera crew to capture predatory fish and dolphins front on as well as get up close to whale sharks.

The crew also used two unmanned submersibles, which allowed them to record footage from 1,000 metres under the Antarctic Ocean, to capture footage of never-before filmed creatures, including hairy-chested Hoff crabs, snub fin dolphins that spit water, and a tool-using tusk fish.