Captain Sir Tom Moore was admitted to hospital on Sunday after being diagnosed with COVID-19, his daughter Hannah revealed on social media.
Sharing a heartfelt message about her father's health to Twitter, she wrote: "I wanted to update everybody that today (Sunday 31st 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."
She went on: "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.
WATCH: Captain Tom Moore receives exciting royal Knighthood news
"The medical care he has received in the last few months 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."
Hannah finished by writing: "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. Hannah x."
The fundraising champion's followers were quick to send their good wishes.
One responded: "Lots of love, respect, well-wishes and gratitude."
The fundraising hero was knighted by the Queen last summer
Others wrote: " We hope that Captain Tom has a quick and full recovery," and: "We’re very sorry to hear this. We are thinking of you all and hoping Captain Sir Tom makes a full and speedy recovery."
Captain Sir Tom raised more than £32 million in 2020 by hitting his target to walk the length of his garden 100 times in honour of his 100th birthday, completing his challenge last April.
He donated the money raised to NHS Charities Together to help frontline workers dealing with the pandemic.
The Captain's birthday was marked by flypasts by the Royal Air Force and the British Army and he was appointed as honorary colonel of the Army Foundation College.
He was knighted by the Queen on 17 July 2020 at Windsor Castle.
Like this story? Sign up to our newsletter to get other stories like this delivered straight to your inbox.