The natural father of Baby P is suing the publishers of a Sunday newspaper for £130,000 damages for printing "one of the gravest libels imaginable".
A judge was told the father, who cannot be named for legal reasons, was wrongly accused in The People of being a sex offender convicted of raping a 14-year-old girl.
The newspaper's publishers, MGN Ltd, later apologised and offered to pay damages.
However, the offer came late and was not enough to compensate the father, referred to as "KC", for the suffering and distress the "completely false" reports had caused, said his QC James Dingemans.
The allegations were contained in two paragraphs in a crime supplement about Baby P's mother, who had separated from KC. They appeared in The People on September 19 2010 in an article entitled "Tortured to death as mum turned a blind eye".
Baby P, later named as Peter Connelly, was just 17 months old when he was found in a blood-splattered cot at his mother's home in Tottenham, north London, in August 2007. He had more than 50 injuries.
Tracey Connelly was jailed in 2009 after admitting causing or allowing his death. Her boyfriend Steven Barker and their lodger, Jason Owens, who was Barker's brother, were found guilty at the Old Bailey of the same charge.
Mr Dingemans said the allegations about the natural father in the wake of the Baby P tragedy were "shocking and appalling". However MGN treated him "as if he didn't really matter".
Heather Rogers QC, appearing for MGN, told the High Court: "This was a mistake that MGN regrets and it has apologised to the claimant, and I repeat that apology on its behalf in this court."
However she denied KC had been badly treated, or that MGN had conducted any kind of "campaign" against him, or dismissed his legitimate complaint.
