Robert Weston was found in the ladies toilet at an Odeon cinema in Birmingham in March 1956.
He has never managed to track down his mother but a DNA database helped him to find his late father's other children, who live in north east Scotland.
Robert discovered he has at least four surviving brothers and a sister. He told BBC Scotland it had been "extremely surreal" to discover he had a long-lost family in Scotland and to speak to his half-brother Tommy Chalmers on the phone. He says meeting them for the first time was the "most profound experience".
Robert met Tommy and half-sister Pat McBain at Inverness airport earlier this month.
He says: "I arrived at the airport and I was really nervous. "I spotted them and I felt my face break into a huge grin. I just had to touch them to make it real."
Tommy, who lives at Burghead in Moray, and Pat, who lives in Banff, took their new brother to meet other relatives, including another brother in Turriff, where their father had lived most of his life.
Tommy's father, Charlie Chalmers, had three young sons with his wife in Aberdeenshire before he went to work in the English Midlands in the early 1950s.
He appears to have had at least one child with Robert's mother, probably living in Rugby or Leicester, before returning to his wife and having three more children.
Tommy says there is an eight-year age gap between his older brothers and him, the eldest of the second set of siblings.
However, he says his father's movements were never discussed in the family. Tommy says: "We sort of suspected something like this over the years.
"There have been one or two things that have cropped up, little things spoken about in the family, but I don't think anybody was 100% sure." Robert and Tommy's father died in 1996.
Tommy says that a letter was found soon after which could have shed light on the identity of Robert's mother.
"I have never seen this letter, however, my sister has and a few others have," Tommy says.
"It was a letter from Rob's mum in 1956 to my father saying that she could not afford to keep the two kids.
"And there was mention of a name, Laurie, and we are not sure if that is male or female or if it is Rob's real name.
"However, this letter has either been mislaid or has gone missing. "If we could find that, we could have a clue to finding Rob's mother."
Robert has no other clue to her identity.
When he was found, at just three weeks old, there was only a brief description of a woman in her mid-20s seen holding a baby in the cinema foyer. Robert, who has recently retired from being a lecturer and lives in Plymouth, has been searching for her for 46 years.
In 2006, a documentary about his quest led to a reunion with Mavis Smith, the 17-year-old girl who had discovered him while she was on a date with her boyfriend.
It was not until Robert's eldest daughter started a Facebook appeal to find her father's family that they got involved with DNA detective Julia Bell. Tommy's second cousin, who was researching her own family history, came up with a close DNA match on one of the genealogy databases.
Ms Bell persuaded her mother, Tommy's cousin, to do a DNA test and the results showed they were getting closer.
All the cousin's uncles were "long dead" so she asked Tommy to take the DNA test and it came up 100% positive.
Robert says he had already been told that his DNA profile suggested he was Scottish but he was "shocked" to finally find and speak to Tommy. "It was a surreal moment," he says.
"I have this guy on the other end of the line, speaking in a Doric accent, who is actually my brother."
Robert says he and Tommy have lived "parallel lives", sharing many of the same interests and experiences such as time at sea. Tommy, who is 58, told BBC Scotland: "We get along really well. "We share a lot of things in common and Rob's the double of my father."