Moore, who will turn 100 later this month, began a JustGiving fundraiser on April 8, initially hoping to raise £1,000 for NHS Charities Together, which raises funds for UK hospitals, including for staff, volunteers and patients affected by the coronavirus crisis.

He completed the challenge on Thursday, after walking 10 laps of his garden each day, aided by a walking frame. He told CNN he never anticipated being able to raise such a sum.

Moore walked 100 lengths of his back garden.

"I'm absolutely overwhelmed by this sum of money -- and when you transfer those into American dollars it's even bigger. We really never, ever for a minute thought we would get to this sort of money. We started off with a little modest figure," he told CNN's Hala Gorani on the "Connect The World" show on Friday.

Born in Yorkshire, northern England, Moore trained as a civil engineer before being enlisted in the British Army during World War II, where he served in India, Indonesia and Britain. He later became the managing director of a concrete manufacturer.

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