It is a tale of illicit love, heartbreaking loss, a cruel twist and a dark family secret that could have come from the pen of Ian McEwan.

A desperate woman uses a newspaper advert to dispose of the son she conceived with her lover while her husband is away fighting for his country.

However, unlike the work of the famously dark novelist, the story of McEwan’s own family has an uncharacteristically happy ending, with the author being reunited after almost 60 years with the brother he never knew existed.

The extraordinary history has came to light after McEwan’s older brother, Dave Sharp, found the advertisement placed in the Reading Mercury by their mother in December 1942. Rose Wort, as she was then called, handed the one-month-old baby David over to his adoptive parents during a brief encounter at Reading railway station.

Mr Sharp stayed unaware that he had been adopted until he was 14. Eight years later his adoptive mother, also called Rose, died but all his adoptive father, Percy, would say when asked about his real family was that they had “got him out of a newspaper”.

It was not until Percy died that Mr Sharp found the advertisement. Between notices for musical instruments and second-hand furniture, it read simply: “Wanted, Home for Baby Boy, age 1 month; complete surrender. Write Box 173, Mercury, Reading.”

But it was an inauspicious time for Mr Sharp: “I was about to get married, buy a new house and get a mortgage, so I put it all on the back-burner for a while.”

He did not pursue the matter until he was 60 and then contacted the Salvation Army’s Family Tracing Service. By the time Mr Sharp traced his natural mother she was suffering from Alzheimer’s disease so could not answer his questions. Then his maternal aunt finally revealed the poignant story behind his mother’s passionate wartime affair with David McEwan, a Scottish army officer, of how she fell pregnant, and her frantic attempts to secure a quick adoption. In a cruel twist Rose’s husband was then killed in the Normandy landings, leaving her free to marry her lover. Six years later Ian was born.

“My mother swore her to secrecy on the way home on the train and she never breathed a word,” said Mr Sharp, 64. “She felt very guilty for telling me and betraying the trust, but also for conspiring against me.”

The sons were to have contrasting lives. David failed his 11-plus and went to the local secondary school before leaving at 15 to train as a bricklayer. Ian spent much of his childhood following their father around the world to army postings before being sent back to board at Woolverstone Hall School in Suffolk.

He went on to take degrees at the Universities of Sussex and East Anglia before becoming one of the Britain’s most successful authors with novels including Enduring Love, The Comfort of Strangers, the Booker Prize-winning Amsterdam and Atonement, which is being turned into a film starring Keira Knightley.

McEwan, 58, has recalled that his mother was tyrannised by his father so he developed a “romantic notion that if the spirit of women was liberated, the world would be healed. . . Pen in hand, I was going to set my mother free”.

For much of their adult lives the brothers lived just a few miles from each other in Oxford. When they finally met Mr Sharp had no idea of his younger brother’s fame.

“I had never heard of him at the time,” said Mr Sharp. “Of course, I’ve read all his books now, but whether he’s a road-sweeper or an author is immaterial. He’s just my brother to me.”

McEwan said last night: “He’s had his say and I’ve had mine. It’s a private matter. It’s no secret.

“David got in touch with our family five years ago and it was a great surprise and pleasure to discover I had another brother.We welcomed him and his family into ours and we keep in touch. We attended his daughter’s wedding last year. I am sad that he never got he chance to know our parents.”

Deborah Rogers, his literary agent, said last night: “The reunion was an extraordinary experience for Ian. The fact he had an elder brother came as a complete surprise.”

Yesterday Mr Sharp said he and his brother were planning to tell their story. “When Ian comes back, we’ll do something together,” he told The Times. He has already started a book about his life called Complete Surrender.

He said he had been happy to surrender the writing to one more experienced in literary matters. “I did suggest that he write it, but he said it was my story and I should tell it.”

Reunited

KT Tunstall, the Scottish singer, found her mother, a former dancer, after she was adopted at two weeks by a family of academics

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