Radio and TV presenter Andrew Marr is recovering in hospital after suffering a stroke, the BBC said.
The 53-year-old broadcaster was taken ill on Tuesday and the hospital confirmed he had a stroke, the corporation said in a statement.
"His doctors say he is responding to treatment," the statement said.
"His family have asked for their privacy to be respected as he recovers. His colleagues and the whole BBC wish him a speedy recovery."
The BBC said James Landale will present The Andrew Marr Show this Sunday.
"We will continue to broadcast The Andrew Marr Show and Radio 4's Start The Week with guest presenters in his absence," the statement said.
Many of Marr's colleagues in the media took to Twitter to express their sympathy.
Fellow BBC politics presenter Andrew Neil wrote: "Very distressed to hear news about Andrew Marr. Best wishes for full and speedy recovery."
Guardian columnist Polly Toynbee tweeted: "Andrew Marr, renaissance man, polymath, wise commentator, painter, runner, brilliant cook - and ace editor. Get well soon. Needed in public life."
Former Tory MP Louise Mensch said: "Joining in the chorus of well-wishers for Andrew #Marr. Hope he has a speedy and full recovery."
Marr, the BBC's former political editor, began his career as a newspaper reporter, becoming the editor of The Independent before turning to television.
He has also presented a number of history programmes along with his politics show and has had five books published.