Lord Ashcroft, the co-author of a controversial biography of David Cameron, missed the book's launch party after suffering from a life-threatening illness.
Call Me Dave, written with journalist Isabel Oakeshott, contained a series of embarrassing claims about the Prime Minister's student days.
One, which was dismissed as nonsense by sources close to the premier, was the allegation that he participated in a stunt while at Oxford University involving a dead pig and "a private part of his anatomy".
Guests at the launch event in London were told that Lord Ashcroft suffered a "life threatening" renal failure, septic shock, liver and kidney failure on September 24 and spent 18 days in intensive care.
A spokeswoman said Lord Ashcroft was now recovering and was "out of danger".