The MP who laid the complaint against Simon Bridges – leading to his demotion last night – is understood to be Waitaki representative Jacqui Dean.
Bridges has been demoted and "relieved of his portfolio responsibilities" following an allegation of serious misconduct relating to an interaction with a female caucus colleague.
National leader Judith Collins announced Bridges' demotion just after 9pm on Wednesday.
It is understood to relate to crude comments Bridges allegedly made at a function about five years ago.
Bridges is understood to have been talking with a group of about three fellow MPs, including Jami-Lee Ross and Todd McClay, when Dean walked past and the Tauranga MP called to her and made the comment.
Dean, 64, complained about it at the time and Bridges was spoken to. She has not spoken publicly on the matter since Bridges' demotion last night and has not responded to requests for comment.
Born in Palmerston North, prior to politics Dean worked in education, as a radio announcer and also once hosted the children's television show Playschool.
She was a former Waitaki District Councillor and deputy mayor, before her election to Parliament in 2005. She served as Minister of Commerce & Consumer Affairs and Minister for Small Business during National's three terms in Government.
"Priorities include keeping pressure on the Government on its failure of Kiwibuild in Wanaka, advocating for infrastructure funding and ensuring locals are well represented in Wellington. Jacqui is passionate about the conservation issues facing the Waitaki electorate such as Wallabies, Wilding Pines and many others," she says about herself on her website.
Dean has previously been outspoken on drug issues and pushed to ban party pills and the smokable plant Salvia.
She is married to Oamaru lawyer Bill Dean. The pair have three adult children and three grandchildren.
'National Party will not tolerate harassment and intimidation'
In a written statement last night Collins said: "This evening, with unanimous support of the board of the National Party, Simon Bridges, Member for Tauranga, has been demoted and relieved of his portfolio responsibilities.
"The decision follows an allegation of serious misconduct relating to Simon Bridges' interaction with a caucus colleague."
It comes as speculation rises that Bridges was preparing to roll Collins as leader of the party.
It is understood Bridges and the National MPs who back him tried to call a caucus meeting on Wednesday night but Collins blocked it.
Some MPs are furious at Collins' move, saying it was "ugly" and "f***ing ridiculous", and a clear bid to halt any leadership bid by Bridges by dredging up remarks from five years ago.
The written statement from Collins said the incident related to comments made by Bridges to a female caucus colleague at a function a number of years ago.
"Having been made aware of the seriousness of the complaint for the first time and the ongoing distress this has caused the complainant, I was left with no option but to immediately demote Simon Bridges and relieve him of his portfolio responsibilities," Collins said.
"This decision has not been made lightly. However, the seriousness of the situation demands a swift and decisive response.
"Under my leadership, the National Party will not tolerate harassment and intimidation of any person.
"Members of Parliament and staff should be able to conduct their duties at all times without feeling unsafe or intimidated, and all deserve to be treated with absolute respect by their colleagues in all situations."
Other caucus colleagues reacted with surprise, when approached by the Herald. One said it was a "complete stitch-up" of Bridges by Collins.
National MPs were already expected to likely have an awkward caucus meeting today after a poll showing Collins had lost the support of both National voters and the country at large.
A Newshub-Reid Research poll asked whether Kiwi voters preferred Bridges or Collins to lead the National Party.
Bridges was backed by 40.7 per cent of voters, with Collins having the support of just 23.3 per cent - the remainder didn't know.