Harry Hogburn always believed his dad, Frederick, a Royal Marine, had died when he was a baby, leaving mum Isabella to raise him as an only child from their home in Dunfermline.
However, he recently discovered his father had moved back to England, where he remarried in 1929 and had a second child, Nora, the following year.
The grandad-of-three – a 91-year-old who lives in Inverleith – only found out about his sister after his daughter, Shirley, and his then-unknown niece, contacted the Wokingham Remembers history society.
The group, which traces the lives of the servicemen, had appealed for information about Frederick, who was originally from the south-east market town, which led to both families contacting it with conflicting details.
Harry said: “It was very emotional to find out I had a sister – when you learn something like that at my age it’s a bit of a trauma to be honest.
“I’d been going 90 years on my own, then to discover this was completely overwhelming. I cried buckets.”
Retired travelling salesman Harry suffers from heart problems and had a chest infection that threatened to stop him from flying.
He defied doctors to make the 40-hour round trip, but needed to be given oxygen on the plane.
Harry, Shirley and his son-in law, Allan Mees, made the emotional journey, with Nora Kazimierczak, 82, waiting to greet them when they arrived at the airport in Perth, Australia.
“I’m quite an emotional person anyway so there were a lot of tears,” Harry said. “I had always wanted to be a brother and there I was meeting my sister for the first time.
“When I met Nora I could see the resemblance straight away. People who have seen the photographs of us together say the same thing, they think we look very alike.
“She has three daughters – two of them live in Australia and the other one in Reading, so I will be meeting her in the summer.
“The family that I have discovered are very pleased about it all as well. It has been delightful to meet them and they are all lovely people.”
Harry and Nora met every day during the two-week trip and he now plans to keep in touch by phone. Shirley, 57, of Livingston, West Lothian – who has a brother, Ian, 53 – said it had given Harry renewed optimism after the death of his wife, Gladys, four years ago.
She said: “His world fell apart when mum died but now he’s met Nora he said it was one of the highlights of his life. To be having this momentous thing happen to you when you’re 91 is just fabulous.”