Royal Navy veteran Steve Aiken has resigned as the leader of the Ulster Unionist Party.
The former nuclear submarine commander's announcement comes amid growing internal concern at his leadership.
Many felt a change was required ahead of next year's Northern Ireland Assembly election.
Decorated British Army veteran and MLA Doug Beattie is viewed as a potential party leadership successor.
Mr Beattie was awarded a Military Cross for bravery during a 34-year career in the Army, and served in Kosovo, Bosnia, Kuwait, Iraq and Afghanistan.
On Twitter, Mr Beattie wrote: "The loneliness of leadership is never easy.
"As my party leader, my colleague and my friend I want to thank Steve for his service past, present and in the future."
Mr Aiken was unopposed in his 2019 leadership bid.
Discussing his time as leader, he said he took pride in the party's decision to take on the challenging health portfolio when power-sharing was restored in 2020.
He said his party colleague, former leader and Northern Ireland Health Minister Robin Swann had been successful in his efforts to tackle the coronavirus pandemic.
Mr Aiken said he will remain in politics and continue as a South Antrim MLA.
Cover image: PA.