Twins adopted by separate parents soon after birth later fell in love and married, unaware they were related, it has emerged.
The marriage was annulled by High Court judges, who ruled it had never been legally valid.
The case emerged during a debate in the House of Lordswhen pro-life campaigner Lord Alton of Liverpool raised the couple's plight to highlight what he said were deficiencies in the Human Embryology and Tissues Bill, making its way through Parliament.
The couple were adopted by different parents and separated soon after birth. They were never told they were twins and did not discover the truth until after their wedding.
Lord Alton, who learned of the case from a High Court judge, is concerned the bill, which makes it easier for lesbian and gay couples to have "test-tube" babies, weakens the rights of children to know their father.
He said: "[The brother and sister] met later in life and felt an inevitable attraction. I suspect that it will be a matter of litigation in the future if we do not make information of this kind available to children who have been donor-conceived."
The bill recognises same-sex couples as legal parents of children conceived through the use of donated sperm, eggs or embryos. Lord Alton said there would be nothing on birth certificates to let children know they had been donor-conceived, and raised concerns that IVF, through which one man can father up to 10 children, would lead to more such cases.
He was worried that the biological identity of one parent could be removed from the birth certificate, and recommended that the child's genetic history should be kept on record to prevent further mix-ups.
"The state is colluding in a deception," he said. "One of the most fundamental things of all is to know who you are. "
Dr Allan Pacey, a lecturer in andrology at the University of Sheffield and secretary of the British Fertility Society, said: "Whether or not you know you are donor-conceived depends on whether or not you are told. But I don't think you need legislation."
