The Archbishop of Canterbury has discovered his biological father was the former private secretary to Winston Churchill.
In a statement, the spiritual leader of the Anglican Communion consisting of some 85 million Christians globally said: "In the last month I have discovered that my biological father is not Gavin Welby, but in fact, the late Sir Anthony Montague Browne.
"This comes as a complete surprise," he added.
The Archbishop said his mother, Jane Williams, and his late father Gavin were both alcoholics when he was a child. His mother has "not touched alcohol for over 48 years," he added.
Archbishop Welby's mother, now married again as Lady Williams of Elvel, said in a statement that she and Gavin Welby had a "short dysfunctional marriage" and that DNA evidence of her son's paternity was "an almost unbelievable shock."
"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," her statement added.
Lady Williams said her son was born nine months after her marriage to Gavin Welby in 1955, adding that the marriage ended in 1958.
The DNA tests were taken after The Telegraph gathered evidence to suggest Browne was Justin Welby's father, the newspaper said on its website.
Rev Welby was installed as the Archbishop of Canterbury in 2013.
