Retiring National Party MP Andrew Falloon is believed to have sent pornographic material to a female teenager.
Leader Judith Collins, who took over from Todd Muller last week, said the party was "advised of an issue relating to Andrew late on Friday afternoon and we have dealt with it this morning".
"Andrew is suffering from significant mental health issues and his privacy, and that of his family, must be respected."
Earlier today, Mr Falloon announced his resignation from Parliament at the upcoming election. This evening a National Party spokesperson told 1 NEWS the incident related to a 19-year-old female.
1 NEWS understands to pornographic material was sent to the teenager after Mr Falloon had been out drinking.
The Prime Minister's office has confirmed Jacinda Ardern received correspondence about Andrew Falloon last week.
It was then revealed National got the correspondence from the Prime Minister's Office after 4pm on Friday night and it was the first National had heard of it, 1 NEWS understands.
The Prime Minister was asked about the correspondence at her post-Cabinet press conference today.
She said she was advised of the “general nature” of it, but was not told the identity of the person who sent the correspondence or which MP it was about.
“My office dealt with it appropriately… Now it sits where it needs to sit, with the National Party,” she said.
Ms Ardern thought there was a 48-hour turnaround from when it was received by the Prime Minister’s office to when it was passed onto National leader Judith Collins.
Mr Falloon is the 13th National MP to announce they won't be standing in September's election, with the decision coming after high-profile MPs Amy Adams and Nikki Kaye said last week they wouldn't stand again.
"As I noted in my maiden speech three years ago, when I was younger I lost three close friends to suicide.
"It was an extremely difficult period in my life. Unfortunately, recently, another friend took their own life, which has brought back much unresolved grief," Mr Falloon said.
"I have made a number of mistakes and I apologise to those who have been affected."
"Recent events have compounded that situation and reminded me of the need to maintain my own health and wellbeing. I have again been receiving counselling."
Mr Falloon is the MP for Rangitata in Canterbury.