Independent unionist MP Lady Sylvia Hermon has announced she will not contest the General Election on December 12.
Lady Hermon has served as the MP for North Down since 2001.
She was first elected for the Ulster Unionist Party, but resigned from the UUP in 2009 over the party's short-lived electoral alliance with the Conservative Party. She successfully retained her seat as an Independent in 2010 and again in 2015 and 2017.
She was also the sole remain voice from Northern Ireland sitting in Westminster after the 2017 election.
Her decision comes days after Sinn Fein and the SDLP announced they would endorse her as the remain candidate in the constituency.
Announcing her decision to retire after 18 years as an MP, she said it has been the greatest honour of her life to serve the people of her constituency.
"It is with enormous sadness that I have decided not to contest the next general election in December," she said.
This has been a particularly difficult decision but, after much thought, I have concluded that it is the right decision for my family and for me at this time. Lady Sylvia Hermon
"During my 18 years as an MP, I have tried hard to balance public and family responsibilities. I owe my family a huge debt of gratitude for allowing me, without ever a word of reproach, to spend so much time at Westminster; they understood how much joy and satisfaction I had from working on behalf of others.
"Now, however, my priorities for the next few years are to spend my time at home in Northern Ireland to see more of my family and to step back from the frontline of public life.
"I apologise most sincerely for any disappointment caused by my decision not to stand.
"Last, but certainly not least, I wish to thank the wonderful staff who have worked alongside me since I was first elected. Their loyalty, friendship and hard work lightened my load, and definitely sustained me through those years.
"If my successor enjoys the role of MP for North Down half as much as I have done, a smile will constantly be on his or her face."
Her decision opens the race to succeed her for the DUP, UUP and Alliance Party.
Born in Dungannon, Lady Hermon is the widow of Sir Jack Hermon, former Chief Constable of the RUC.