Sir Denis Thatcher, the husband of Lady Thatcher, former Conservative Prime Minister has passed away piecefully the family has announced.
The 88-year-old, who had heart surgery in January this year, returned to hospital after feeling unwell two weeks ago.
He died at the Lister Hospital in London.
Remembering Sir Denis
A spokesman for the Thatcher family said: "It is with deep sadness that we have to announce that Sir Denis Thatcher passed away peacefully this morning in the Lister Hospital after a short illness.
"His family were with him at his bedside when he died."
The union flag at Conservative central office in London was lowered on Thursday in a mark of respect for Sir Denis.
Sir Denis had originally been at the Royal Brompton Hospital, where doctors had said they wanted him to have more tests when he was readmitted to hospital as a "precautionary measure".
He was later transferred to the Lister Hospital.
He was said to have been in good spirits and had received several visits from Baroness Thatcher.
His son Mark had flown to London from his home in South Africa to be at his father's bedside.
Sir Denis was in buoyant mood when leaving hospital earlier this year
His daughter Carol, who spends much of her time in Switzerland, is also in London.
Although he had enjoyed success as a millionaire businessman, Sir Denis public fame owed most to his marriage to Margaret Thatcher.
His motto in that role was the prime ministers' consorts should be "always present, never there".
Sir Bernard Ingham, Baroness Thatcher's former press secretary said: "I am extremely sad that he has died. I have very many fond memories of him as the prime minister's consort and husband.
"He was extremely loyal and supportive in that position. He was in fact a manifest role model for any prime minister's consort."
Lady Thatcher said of her husband in her autobiography, "The Downing Street Years": "I could never have been prime minister for more that eleven years without Denis by my side.
"He was a fund of shrewd advice and penetrating comment. And he very sensibly saved these for me rather than the outside world."
Sir Denis left hospital 11 days after his heart by-pass, with doctors calling the operation a "complete success".
At the time his daughter put his quick recovery down to "copious gin drinking".
Last year, Baroness Thatcher turned down an invitation to visit the Falklands, saying the trip would have been "too gruelling" for her husband.
The trip would have marked the 20th anniversary of the battle to recapture the islands.
Sir Denis is said to have been the key influence in persuading his wife to bow out of public speaking after she suffered a series of slight strokes.
She has defied doctors, however, by attending a number of functions.
Baroness Thatcher said she could not have made it to the top without him.
They were married for more than 50 years, including 11 at Downing Street.
My sincere condolences go to Lady Thatcher and her family. R.I.P Sir Denis.