Warning: This article discusses suicide.
Newshub can reveal Prime Minister Jacinda Ardern was alerted by an individual about an incident involving National MP Andrew Falloon.
The Prime Minister's Office passed on the correspondence from the individual to the leader of the Opposition Judith Collins last week with the permission of the correspondent.
The Prime Minister's Office says it treats all correspondence with confidentiality and all matters to do with Andrew Falloon's resignation are a matter for the leader of the Opposition.
The MP for Rangitata announced his resignation in a statement on Monday, explaining that he will not be contesting the upcoming election to focus on his mental health.
"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," Falloon said.
"Unfortunately, recently, another friend took their own life, which has brought back much unresolved grief. I have made a number of mistakes and I apologise to those who have been affected."
Falloon did not disclose what those "mistakes" were.
"Recent events have compounded that situation and reminded me of the need to maintain my own health and wellbeing," Falloon added. "I have again been receiving counselling."
Newly-appointed National Party leader Judith Collins said Falloon had advised her that he planned to step down.
"The National Party was advised of an issue relating to Andrew late on Friday afternoon and we have dealt with it this morning," she said in a statement.
Collins did not provide details on what the "issue relating to Andrew" was.
"Andrew is suffering from significant mental health issues and his privacy, and that of his family, must be respected."
Falloon thanked Collins for her support and said he is looking forward to helping a new candidate in the Rangitata electorate in "any way" he can.
"I apologise for this disruption to my colleagues and to those I serve in mid- and south-Canterbury."
Falloon is the 13th National MP to announce they won't stand at the election.
Last Thursday two senior National MPs, Nikki Kaye and Amy Adams, announced they would stand down after the election - just days after Collins became leader.
Collins became leader after Todd Muller suddenly resigned last Tuesday, saying the role had "taken a heavy toll" on him personally and that it had "become untenable from a health perspective".
Muller plans to stay on as an MP but is taking some time off.