The archbishop of Canterbury, leader of the Church of England, said on Friday that a DNA test had revealed that his biological father was not the whiskey salesman who had married his mother, but the man who had been the last private secretary for Sir Winston Churchill.

In an unusually frank statement on his website, the Most Rev. Justin Welby said he had discovered the truth “in the last month,” after taking the test.

“This comes as a complete surprise,” he said.

The archbishop said his father had been a British diplomat, Sir Anthony Montague Browne, who served as a private secretary to Churchill in the last years of his life. Churchill, who was the prime minister of Britain, died in 1965. Mr. Browne died in 2013 at age 89.

Archbishop Welby, 60, said that he had long believed his father was Gavin Welby, whom his mother married in 1955, and that he had released his statement because of “media reports” on the matter. The revelation was reported by The Daily Telegraph, which said it had “pieced together evidence” about the archbishop’s father and had presented that evidence to him.