Rob Weston, 61, went six decades not knowing whether he had any siblings until he found out about Tommy Chalmers, 58, last year.
Rob was abandoned by his mother in the women’s toilets in a cinema in Birmingham 61 years ago and was left in the dark about his wider family.
But after looking into a national DNA database, the university lecturer was able to trace his family roots back to Turriff, Aberdeenshire.
Following his discovery and initial meeting with Tommy, he found another brother residing in Wales called Larry Aston.
Extensive research in recent months has led to the discovery of Rob’s birth certificate, which revealed he was originally named Paul Aston.
It has also confirmed that his mother, who died in 1961, was called Betty. Rob was also reunited with Bryn Jones, who was born from a later relationship of their mother’s.
He said: ‘It’s all been mind-boggling and a bit numbing. I was just kind of getting used to the idea of having Tommy when we discovered Larry. It’s a lot to take in and has taken some time to adjust to.
‘The birth certificate has actually revealed I’m nine days younger than I thought it was. At least it went in the right direction.’
Rob was adopted as a baby and began searching for his blood family in the 1970s without success.
Tommy Chalmers, from Burghead, Moray, had planned a series of north-east get-togethers but the publicity around their story left his clan bowled over a second time after it led to the discovery of another sibling with whom they share a father.
Larry Aston, who lives in north Wales, and Mr Weston, who lives in Plymouth, both travelled to the family’s hometown of Turriff to meet with relatives.
The reunion has raised suspicions there may also be a sister to be tracked down who has the late Charlie Chalmers – who moved temporarily to England for work in the 1950s – as a father.
Security guard Tommy said media attention for their intriguing story had helped lead them to Mr Aston.
He said: ‘A guy in Canada saw the story and he has a second cousin called Larry and made the connection.
‘We managed to get in touch and got him to do the DNA test. We’ve got the results back now and he’s a full brother for Rob and a half-brother for ourselves.
‘Larry’s come from different sources and he always thought that he had a sister, he was never searching for a brother. He knew nothing about Rob.’