Lifted from a BBC news report today:

A pair of twins who were adopted by separate families as babies got married without knowing they were brother and sister, a peer told the House of Lords.
A court annulled the British couple's union after they discovered their true relationship, Lord Alton said.
The peer - who was told of the case by a High Court judge involved - said the twins felt an "inevitable attraction".

'Truth will out'

The former Liberal Democrat MP raised the couple's case during a House of Lords debate on the Human Fertility and Embryology Bill in December.

"They were never told that they were twins," he told the Lords.

"They met later in life and felt an inevitable attraction, and the judge had to deal with the consequences of the marriage that they entered into and all the issues of their separation."

He told the BBC News website that their story raises the wider issue of the importance of strengthening the rights of children to know the identities of their biological parents.