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GROWING up, Martijn van Halen couldn’t help but notice the stark differences between him and his father - so it came as little surprise to him when he was told he was conceived via a donor.

But then things took an unexpected turn when he discovered the shocking truth about his conception. The donor had in fact been a Dutch fertility doctor who had secretly used his own sperm to impregnate unsuspecting women.

And Martijn, 44, reveals he has more than a hundred half-siblings in a WhatsApp group he set up - and suspects there could be dozens more.

Speaking exclusively to The Sun, he says: “In my group we have 102 people who have all matched to his DNA.

“We can only know for sure if they test their DNA. There are still a lot of people who don’t even know they were donor conceived.