The Sun newspaper has strongly denied accessing former Prime Minister Gordon Brown's family medical records without his knowledge.
The paper said a story in 2006 that Mr Brown's son Fraser had cystic fibrosis came from a member of the public.
The Sun has released a video interview with the unidentified man who it says was the source.
A spokeswoman for Mr Brown said in response: "The matter is now in the hands of police."
Mr Brown said he was left "in tears" when he was told that the Sun was publishing the story.
He said he did not know how the newspaper got access to the details but said: "I can't think of any way that the medical condition of a child can be put into the public arena legitimately unless the doctor makes a statement or the family makes a statement."
The paper said the man's own child also had cystic fibrosis and he wanted to raise awareness of the condition.
The man told the Sun: "I felt vindicated in contacting the Sun.
"I just felt at the time that we could have made something positive out of the tragedy and I believe the truth would have come out eventually anyway."
The Sun, published by Rupert Murdoch's News International, said it had conducted an inquiry into the allegations and that it had not accessed the medical records of Mr Brown's son or commissioned anyone to do so.
In a statement, the paper said: "The story originated from a member of the public whose family has also experienced cystic fibrosis.
"He came to the Sun with this information voluntarily because he wanted to highlight the cause of those afflicted by the disease.
"The individual has provided a written affidavit to a lawyer confirming this.
"On receipt of the information, the Sun approached Mr Brown and discussed with his colleagues how best to present it.
"Those colleagues provided quotes which were used in the published piece which indicated his consent to it."
But the Cystic Fibrosis Trust questioned the decision to publish the information "without express permission, regardless of their motivation".
A spokesman said: "The release of any medical information to the media or anyone else is a decision for patients or, in the case of children, their parents to make."
The Sun used the front page of Wednesday's edition to rebut Mr Brown's claims about the alleged accessing of his son's medical records.
Mr Brown said he was "disgusted" by the conduct of News International's newspapers and accused them of having links to criminals.
The Sunday Times, another News International title, rejected this and said it had not broken the law in a story about a flat bought by Mr Brown.
News International is under continuing pressure despite its decision to close the News of the World amid allegations its journalists hacked the phones of murder victims and bereaved service families.
The Commons Culture Committee has asked Mr Murdoch, his son James and News International chief executive Rebekah Brooks to appear before them next week to discuss the allegations and the internal inquiry currently taking place at the company.
News International has said it will "fully co-operate" with the committee but has not confirmed whether they will attend.