Captain Tom Moore, who raised £32 million for the UK"s National Health Service, has been admitted to hospital with Covid-19, according to his family.
The 100 year-old is being treated in hospital yet has not been admitted to ICU.
In a statement posted on Captain Sir Tom Moore's Twitter page, his daughter said: "I wanted to update everybody that today (Sunday 31 January) my father was admitted to hospital. "Over the last few weeks he was being treated for pneumonia and last week tested positive for Covid-19.
"He was at home with us until today when he needed additional help with his breathing. He is being treated in a ward although he is not in ICU.
"The medical care he has received in the last few weeks has been remarkable and we know that the wonderful staff at Bedford Hospital will do all they can to make him comfortable and hopefully return home as soon as possible.
"We understand that everyone will be wishing him well. We are of course focusing on my father and will update you when we are able to."
The message was signed off "Hannah x".
It is not clear whether the veteran has been vaccinated, and there is no mention that he has had the jab on his social media pages.
Keir Starmer, the leader of the British Labour Party has tweeted his support for the veteran commenting: "The whole nation hopes you get well soon Captain Tom Moore. You've been an inspiration to us all throughout this crisis."
Vaccine Minister Nadhim Zahawi tweeted that he was "praying" for Captain Sir Tom Moore.
Capt Sir Tom's fundraising efforts raised more than £32 million ($61m) for the NHS, walking 100 laps of his garden before his 100th birthday during the UK's first national lockdown in April.
The veteran set out to raise £1000 from his lockdown charity challenge but his efforts struck a chord with the nation, and praise and donations flooded in.
In acknowledgement of his efforts, he was knighted by the Queen during a unique open-air ceremony at Windsor Castle in summer 2020.