The Archbishop of Canterbury has said it was a "complete surprise" to find out that his real father is Sir Winston Churchill's last private secretary.

The Most Rev Justin Welby, who thought his father was Gavin Welby, recently discovered his biological father is in fact the late Sir Anthony Montague Browne.

A DNA test showed a 99.9779% probability they were father and son.

Mr Welby decided to take the test after The Daily Telegraph spoke to Lady Montague Browne, Sir Anthony's widow, who said she had been aware her husband may have had another child.

She said she noticed a resemblance between her husband and the Archbishop after she saw Mr Welby on television.

The Archbishop said his experience is "typical" of many people, adding: "To find that one's father is other than imagined is not unusual."

In a statement, Mr Welby added: "This revelation has, of course, been a surprise, but in my life and in our marriage Caroline and I have had far worse.

"I know that I find who I am in Jesus Christ, not in genetics, and my identity in him never changes.

"Even more importantly my role as Archbishop makes me constantly aware of the real and genuine pain and suffering of many around the world, which should be the main focus of our prayers."

Mr Welby said his mother Jane Williams and Gavin Welby were both alcoholics, adding his mother had been in recovery since 1968, and had not touched alcohol for almost 50 years.

Gavin Welby, a whisky salesman, died "as a result of the alcohol and smoking" in 1977 when Mr Welby was 21.

"As a result of my parents' addictions my early life was messy, although I had the blessing and gift of a wonderful education, and was cared for deeply by my grandmother, my mother once she was in recovery, and my father (Gavin Welby) as far as he was able," Mr Welby said.

Lady Williams said the news had come as an "almost unbelievable shock" as her son was born almost nine months to the day after she married Gavin Welby in the US in 1955.

She said her then-husband was putting pressure on her to leave her job as personal secretary to the Prime Minister and run away with him at the age of 25.

In a statement she said: "One feature of this pressure is that I was already drinking heavily at times.

"Although my recollection of events is patchy, I now recognise that during the days leading up to my very sudden marriage, and fuelled by a large amount of alcohol on both sides, I went to bed with Anthony Montague Browne.

"It appears that the precautions taken at the time didn’t work and my wonderful son was conceived as a result of this liaison."

Lady Williams said she saw Sir Anthony occasionally after her marriage to Gavin Welby broke up in 1958, but that he gave no hints he might have thought he was the Archbishop's father.

Sir Anthony died in 2013.