Mike Nesbitt has quit his role in a top Stormont committee after flouting lockdown rules by travelling to the north coast to stay with a "female friend".
The former Ulster Unionist Party leader admitted he had made some "very poor decisions" and confirmed he had been living apart from wife, Lynda Bryans, since January.
Mr Nesbitt (62) said it had been a "stressful and difficult period" and apologised over revelations he had made a number of recent trips to stay at a property in Portballintrae, Co Antrim.
Lockdown regulations, outlined by his party colleague, Health Minister Robin Swann, advise against unnecessary journeys in a bid to stem the spread of the deadly and highly contagious coronavirus, which has killed hundreds of people across Northern Ireland.
Mr Nesbitt had tweeted his support for the health service throughout the course of the Covid-19 crisis, and his Twitter profile picture has featured the NHS logo.
"This has been a stressful and difficult period for me and unfortunately I have made some very poor decisions," said Mr Nesbitt. "I am remorseful and apologise. I shall not return during lockdown."
Speaking to the Sunday World newspaper, the MLA for Strangford told how he had tendered his resignation as Deputy Chair of the Committee for The Executive Office, which advises government ministers.
His party leader, Steve Aiken, accepted his resignation and criticised the former broadcaster in a statement.
"Breaking the lockdown regulations is totally unacceptable, no matter who you are," he said. "The rules are there to help save lives. Mike has made a huge mistake and he has accepted what he did was wrong.
"I have accepted his resignation as Deputy Chair of the Committee for the Executive Office. The lockdown rules are there to help save lives and the message remains the same. Stay home, protect the NHS, save lives."
It is understood Mr Nesbitt will continue in his role as an MLA.
Confirming he was no longer based at the east Belfast home he had shared with wife of 28 years, former UTV presenter Ms Bryans, Mr Nesbitt said he had been living alone in rented accommodation since "well before lockdown".
Last Tuesday, Mr Nesbitt had told Radio Ulster's Talkback programme he had been clearing out his attic.
But he told the Sunday World: "Since late January, well before lockdown, I have been living alone in a rented room in accommodation far north of Belfast. Recently I have stayed occasionally in a three-bedroom property occupied full time by a female friend."
Since lockdown measures were announced across the UK on March 23, the message from government has advised strongly against any unnecessary travel.
Last month, Health Minister Mr Swann said: "It is essential that these tight restrictions are rigorously maintained in the weeks ahead. Quite simply, lives depend on it. So, let me appeal to everyone not to slip back into old habits. Any signs of complacency and impatience must be strongly resisted."
According to the Sunday World, Mr Nesbitt was in Portballintrae on the weekend Belfast-born Scottish Chief Medical Officer Dr Catherine Calderwood was caught visiting her holiday home in Earlsferry in Fife, more than an hour's drive from her main Edinburgh home. She later resigned.
The Sunday World claimed Mr Nesbitt did not return to the north coast the following weekend, but was back a week later and has returned several times since.
On Sunday night, he said he did not want to make further comment.
Earlier this year, Mr Nesbitt told of his loss after his mother, Brenda Nesbitt, known as Paddy, passed away in February, just short of her 94th birthday. "Mum was a people person and no people were more important than her family," he said last month.
Cambridge-educated, journalist, broadcaster, Victims' Commissioner, Unionist Party leader, MLA, mental health campaigner - a brief rundown of Mike Nesbitt's impressive CV.