Prince William donated a substantial amount to the fundraiser of the veteran Captain Tom Moore, who went viral this week. He is this 99-year-old World War II serviceman who wanted to raise money for the NHS.

Moore originally planned on raising $1,250 (£1,000) for the NHS Charities Together by making 100 laps in his garden before he turned 100 years old on April 30. The elderly, who needs a mobility device to walk, inspired people to donate to his cause via his JustGiving page.

One of these people is Prince William, who said that the Moore is an "absolute legend" and a one-man fundraising machine. According to reports, the Duke of Cambridge made a secret donation to Moore's cause. Kensington Palace confirmed that the royal did contribute to the captain's fundraiser.

To date, Moore has raised $22.5 million (£18 million) after his story went viral. Some 950,000 have contributed to his initiative.

As a result, the public has backed a petition for the captain to receive knighthood from the Honours Committee. So far, more than 500,000 have signed the petition. Prime Minister Boris Johnson's office said that they will find ways to honor the veteran properly amid calls of making the elderly a knight.

In an interview with BBC, Moore said that he did not imagine the enormous result of his cause. He thanked everyone who donated their money and made a special mention to Prince William, after he heard the duke commend his efforts, which aired in the news.

"It's absolutely amazing that my super prince can say something like that," the veteran war hero said. 

Moore did his final laps around his garden on Thursday but he said that he is still willing to walk if people are going to keep donating. He picked the NHS as the recipients because the doctors and nurses have been helping him with his cancer treatment and broken hip for many years. 

The veteran was supposed to have a big party for his 100th birthday but it has since been canceled since the lockdown orders in the U.K. He said, however, that the outpouring of love and support from the public was better than the party.

Meanwhile, the Duke and Duchess of Cambridge also wrote to Moore. The contents of the letter were not disclosed but Prince William and Kate likely thanked and praised the veteran for what he did. The man from West Yorkshire is now considered a national treasure.