After uploading his DNA to a genealogy site, he matched 100 percent with another son of the singer.
60s legend Lulu told Louis Theroux in his latest podcast that she only recently learned about the existence of another son of Maurice, and that he may have been born as a result of an affair during their marriage.
57-year-old Nick Endacott-Gibb insists that he was conceived about two years before Lulu and Maurice's affair began.
He told the Mirror: "I was born in April 1968, conceived in August 1967. Lulu and Maurice only got married in 1969, after what has been described for decades as a 'tumultuous' romance.
"Were you with him, Lulu? Two years is not a tumultuous romance. I’m just as curious as she is whether Maurice was with her at the time I was conceived. After all, it was the summer of love!"
Nick, who lives in Hove, was adopted from an orphanage at 18 months by secretary Peggy and her husband David, a qualified surveyor.
Nick's biological mother is former music studio manager Patti Nolder, whom he met in 2003 by uploading his details to the Missing You database — a long-standing online community similar to a forum that helps reunite families.
Initially, she told him that his father was Chris Andrews, guitarist and vocalist of the 60s psychedelic pop group The Fleur de Lys, but a DNA test confirmed otherwise.
It was Patti's sister who suggested the name Maurice to him, and after uploading his DNA to a genealogy site, he matched 100 percent with another son of Maurice, Adam, who also uploaded his DNA.
This was followed by matches with the Gibb cousins, and Nick formed close relationships with their older sister Lesley and her daughter Debbie, who live in New South Wales, Australia.
Nick never got to meet Maurice before his death from a heart attack in 2003, but he said: "I’m sad that he died before I got to meet him, but his memory lives on in the songs."
Lulu was married to Maurice for six years, and their relationship officially ended in 1975. They had no children.
She admitted that the news of Nick's existence came as a complete surprise to her decades after their relationship ended.
Louis said: "You know, we’re not always the best versions of ourselves, and Maurice, I think it’s now widely acknowledged, had an affair with Barbara Windsor while he was with you."
