Sinn Féin president Gerry Adams has initiated defamation proceedings against the BBC over a programme in which it was alleged he sanctioned the murder of an IRA double agent.
The case is being taken in the High Court in Dublin, the Irish Independent has learned.
In the programme, an anonymous man claimed Mr Adams sanctioned the killing of Denis Donaldson (55), a former Sinn Féin official who was exposed as a British spy - having worked for MI5 for two decades.
He was shot dead at his isolated cottage near Glenties, Co Donegal, in April 2006.
The explosive claims about the Louth TD were aired on a BBC Northern Ireland 'Spotlight' programme in September last year.
The man who made the claims said he was a paid state agent in the IRA.
Mr Adams indicated at the time that he intended to sue the BBC.
The proceedings were initiated on Tuesday and Mr Adams is being represented by high-profile defamation lawyer Paul Tweed, of Johnsons Solicitors.
Sinn Féin referred a request for comment to Mr Tweed's office last night.
However, Mr Tweed was unavailable.
Mr Adams vehemently denied the claims in the aftermath of the broadcast.
"It's wrong. I repudiate it, deny it absolutely and categorically and specifically," he said at the time.
In the aftermath of the broadcast, Mr Adams attributed the claims to "elements within the British system" trying to undermine him and his party.
"We have to look at what's behind this agenda," he said.
"The person who made this allegation - an anonymous, unnamed, self-professed agent of the British state.
"So whose agenda is that serving? This is an attempt to rewrite history.
"There are elements within the British system who will never be reconciled with the fact that we have got a peace process and that Sinn Féin is in the leadership of that process, along with others."
The BBC has previously stated it stands by its journalism, but no comment was forthcoming from the broadcaster last night.
The dissident republican group the Real IRA claimed responsibility for Mr Donaldson's murder in 2008.
No one has ever been prosecuted in connection with his death.