Dunderdale told CBC's "On Point Radio" that backbencher Tom Osborne asked for a greater role in her government last March and privately backed her leadership.
The member for St. John's South shocked political circles Thursday when he quit to sit as an Independent, saying he never supported Dunderdale as party leader. It's the first major crack in the Progressive Conservative caucus armour as its popularity and that of the premier continue to slide, according to recent polls.
"We have never heard any of this from Mr. Osborne until yesterday," Dunderdale said Friday. "I don't disbelieve anything that Mr. Osborne is saying, however, the private message has been distinctly different from the public message.
"In March of this year, he was asking essentially to come back into cabinet. And that's a strange thing to do with a leader you don't support."
Osborne flatly denied the premier's version as the dispute devolved into a he-said-she-said affair. Tory ministers and backbenchers took turns Friday publicly deriding Osborne as "disengaged" and even "deadwood."
"At no time did I lobby for a cabinet position," Osborne said in an interview Friday. The discussion he had with Dunderdale was about playing a more active role in government, including speaking engagements for various ministers, he said.
"The reality is, I had issues with leadership and the party can't have it both ways. They can't ... have members coming out and saying that I was disengaged for the past year-and-a-half or two years, and at the same time saying that I was quietly supporting the leadership and lobbying for positions."
Dunderdale's office did not respond to an interview request Friday. She had agreed to the "On Point Radio" appearance before Osborne announced his move.
Osborne served as health and justice minister under former Tory premier Danny Williams before he was dropped from cabinet in 2007 after what he said was a heated disagreement.
Despite that rancour, Osborne said he still respected Williams as leader.
Dunderdale, who took over in late 2010 when Williams suddenly left politics, says Osborne supported her bid for the party helm when she called every member of caucus.
She said she phoned Osborne "to give him an opportunity to express any reservations he might have about my leadership. He didn't do any of that. He, in fact, said that he would support me if there was a leadership bid."
Osborne's recollection of that phone call was that he openly told Dunderdale that he had urged another senior cabinet minister to run. But none of the obvious contenders stepped up to replace Williams, one of the most popular premiers Canada has ever seen.
"I told her straight up that I had concerns, that I was lobbying for somebody else, but that she's now the only choice for leader and that, you know, I was going to give her the benefit of the doubt ... and support her," Osborne said.
His departure leaves a majority government of 36 Progressive Conservatives versus six Liberals and five New Democrats.
It also coincides with a looming debate in the legislature and the pending release of updated cost estimates for the planned $6.2-billion Muskrat Falls hydroelectric project in Labrador. Dunderdale's government has championed what critics say is a risky and expensive venture, and will decide in coming months whether to approve it.
Osborne, first elected in 1996, says he will consider joining the Liberals or NDP after consulting his constituents.
He was re-elected as a Tory last October but says he and many of his supporters are unhappy with Dunderdale's leadership and what he describes as her tight grip on communications.
In particular, Osborne said he regrets voting for contentious Bill 29 last June. Legislation that was blasted by access-to-information watchdogs as a regressive clampdown on government documents passed after a four-day filibuster by opposition members.
Osborne says he toed the government line out of fear of repercussions that could work against his constituents.
Dunderdale said Friday that Osborne was never threatened with such reprisals.
"Absolutely not," she said, adding that he never raised such concerns in caucus.