The video, posted by Giles Martin, who followed in his late father's footsteps and is also a producer and songwriter, shows Sir George explaining his first impressions of the Fab Four.

After being told about the band, he thought: "Well, that's a silly name for a start. Who'd ever want a group with the name Beatles?"

But he agreed to meet them and the band travelled to London from Liverpool, he tells his granddaughter in the clip.

Martin, who later became one of those associated with the group known as "the Fifth Beatle", continues to explain how he was won over by their "magic".

"When I listened to what they did, it was okay, but it wasn't brilliant," he says. "It was okay, you know. So I thought, why should I be interested in this?

"But, the magic came when I started to get to know them, because they were terribly good people to know. They were funny, they were very clever... and they were the kind of people that you like to be with.

"And so I thought, well, if I feel this way about them, other people will feel this way about them. So therefore, they should be very popular."

Sir George died in March 2016, aged 90. At the time, Sir Paul McCartney said: "He guided the career of The Beatles with such skill and good humour that he became a true friend to me and my family. If anyone earned the title of the Fifth Beatle, it was George."

Posting the video of his father and daughter, Giles Martin said: "I don't normally share anything personal but this my dad from a while back explaining to my daughter he signed the Beatles.

"Ordinary people do extraordinary things. Great decisions are made for the simplest reasons."

The story of The Beatles' last ever live performance, up on the rooftop of 3 Savile Row, was recently charted in Peter Jackson's three-part documentary Get Back, which was released in November.