The Stormont Assembly has been plunged into crisis after all non-Democratic Unionist members walked out ahead of a disputed statement by the North's First Minister on her role in a botched renewable energy scheme.
In unprecedented schemes, DUP leader Arlene Foster addressed row upon row of empty benches in Parliament Buildings in Belfast, with only party faithful remaining in the chamber in the seats behind her.
The bitter row unfolded after Sinn Féin Deputy First Minister Martin McGuinness withdrew his approval for Mrs Foster to appear to explain her role in an error-ridden scheme that has left the Northern Ireland taxpayer facing an overspend bill of an estimated £400m.
All statements by Mrs Foster and Mr McGuinness's joint office need the support of both sides of the powersharing executive.
Mr McGuinness's move prompted members from all parties, but the DUP, to question the validity of Mrs Foster's appearance.
The Sinn Féin veteran said her remarks could only be viewed as a personal statement.
When she did rise to her feet, Mrs Foster reiterated her apology for not introducing cost controls in the Renewable Heat Incentive (RHI).
The DUP leader said it was the deepest regret of her time in office.
"Not for one minute do I want to shirk or avoid responsibility," she added.
Before the extraordinary walkout, Mr McGuinness told the media: "The statement does not have my authority or approval as Deputy First Minister.
"She is speaking in a personal capacity and not in her role as First Minister."
After Mrs Foster's statement, the Assembly is due to debate an SDLP motion of no confidence in the First Minister.
The row threatening the peace-building institutions has erupted over the controversial energy scheme - set up by Mrs Foster - which paid out subsidies well in excess of the costs of buying renewable fuel.
Claims of widespread abuse include a farmer allegedly set to pocket around £1m in the next 20 years for heating an empty shed.
The "cash for ash" scandal reached fever pitch last week when former DUP economy minister Jonathan Bell broke ranks to level a series of explosive claims against his leader and party advisers.
In an extraordinary TV interview, a tearful Mr Bell said God told him to come clean as he claimed a "highly agitated and angry" Mrs Foster demanded he keep the RHI open for an extra fortnight despite its huge losses.
Mrs Foster strongly rejected the claims. Mr Bell was suspended by the party over the weekend.
Today, Mr Bell claimed he had an email in his possession that contained critical information about the scandal.
He said he was being prevented from publishing details of the message and called for that ban to be lifted.
Much of the scrutiny on Mrs Foster has focused on how she responded to concerns raised by a whistleblower during her time as economy minister.
There was a flurry of claims and counter claims last week on whether the individual raised concerns directly to Mrs Foster, or if she only outlined them after Mrs Foster passed her on to meet with her officials.
The DUP published an email from the whistleblower last week that made no mention of her RHI concerns - the party cited it to demand an apology from those who had asserted she should have done more.
However, another email has since emerged, that was sent directly to Mrs Foster in 2013, that did raise specific concerns about the scheme.
Addressing the issue in the chamber, Mrs Foster said her former economy department owed the whistleblower an apology.
"She deserves our high respect and a sincere apology on behalf of my former department, which should not have dismissed her claims with disbelief, but examined them with diligence," she said.
"It is no exaggeration to say that had she been listened to on any of the three occasions when she approached DETI, this crisis would have been avoided."
In regard to what information was passed directly to her, the DUP leader added: "Unfortunately, it has been difficult to establish the exact facts around contact between this concerned citizen and myself and the department."