He is only the fourth person in the world officially classed as male to have had a baby.
The man, in his 30s, was born female but underwent sex-swap surgery later in life. Despite the operations, he still had a womb and was able to get pregnant.
The unnamed man was said to be from the West Midlands and in a long-term relationship.
Last night an expert confirmed that the case — four years after American Thomas Beatie became the world's first-ever pregnant man — was "unique" here.
Joanna Darrell, speaking on behalf of transgender support group The Beaumont Society, said: "As far as we know there is only him."
She told how the man gave birth to a boy last year after seeking guidance from the society about getting pregnant.
The organisation referred him to charity the Gender Identity Research and Education Society.
Despite going under the knife to become a man he had asked surgeons not to remove his womb — as is usually the case in such ops.
It meant his woman's reproductive system could be reactivated using treatment with female hormones.
Joanna said: "He got back in touch about six months ago to thank the society for its help. He said he had had the baby."
The boy is believed to have been delivered in a Caesarean op — although medics said that a natural birth could still have been possible.
The Human Fertilisation and Embryology Authority yesterday refused to disclose if it knew about the birth.