Brisbane - Australia coach Ewen McKenzie has said there was a "bunch of reasons" but refused to go into details after he sensationally quit following a narrow loss to the All Blacks on Saturday.
McKenzie, who has been hit by speculation over player discontent and his private life, said he sent an email announcing his resignation earlier on Saturday.
Australian Rugby Union (ARU) chief executive Bill Pulver announced the shock resignation shortly after Saturday's narrow 28-29 defeat to New Zealand in Brisbane.
"I resigned this morning at 10 o'clock. I wrote to Bill (Pulver) and the board members and discussed what's been going on," McKenzie said in brief comments to media.
"I've been a very proud contributor to Australian rugby. There's a bunch of reasons that I've put in writing to Bill.
"My intention was to resign win lose of draw. I've only just told the team. I didn't advise the team or staff before the game.
"It's been a disappointing time for a number of reasons. I'm not going to go into the details, you guys can work it out.
"I've been unhappy with a bunch of things and the easiest thing for me is to exit stage left. I'll leave you guys to speculate or ponder, I'll write a chapter in my book."
Pulver said he tried to talk McKenzie out of resigning and hit out at the "character assassination" that he said the coach had suffered, calling it "unfounded".
"Australia has lost a terrific coach and a great bloke, and it is extremely disappointing that a Wallaby coach feels he needs to resign from his position particularly when you look at the way they played tonight," Pulver said.
"I received an email from Ewen at 10am this morning with a letter of resignation. I immediately asked for a meeting with him and tried to talk him out of the decision and sought an explanation as to why he had done this with obviously a playing group of the calibre you saw tonight and a runway leading to (next year's) Rugby World Cup.
"Ewen said that he felt he was going to struggle to maintain the level of respect he needed from the playing group and his support staff, really directly in my view because of the extraordinary character assassination that he has had to put up with over the last two weeks."
- 'Attack was relentless' -
McKenzie was last week forced to deny speculation of an intimate relationship with a female staff member at the centre of disciplinary proceedings facing back Kurtley Beale.
Beale has been suspended following an on-flight argument with the staffer and claims that he sent offensive text messages about her. She has since quit the Wallabies set-up.
Wallabies captain Michael Hooper and vice captain Adam Ashley-Cooper have voiced both said they hoped Beale would not be sacked over the incident.
Pulver said: "As somebody who is basically the custodian of this game and really responsible for upholding the core values of the game of passion, discipline integrity and respect, what's happened to Ewen over the past two weeks is extremely disappointing.
"Despite clarifications around the circumstances, the attack on Ewen was relentless and essentially left him with the view that he couldn't continue in the role because it was just too far back in order for him to achieve the level of support from the playing group and support staff that he needed to be an effective Wallaby coach."
He added that Australia were yet to approach a possible replacement, although the Wallabies hope to secure a new coach before leaving for their European tour on Friday.