Washington (CNN) Former Department of Veterans Affairs Secretary David Shulkin said Monday that White House chief of staff John Kelly called to give him a heads up that he'd be fired via a tweet from President Donald Trump.

"General Kelly gave me a heads up that the President would most likely be tweeting out a message in the very near future, and I appreciated having that heads-up from General Kelly," Shulkin told CNN's Alisyn Camerota on "New Day," describing the events of last Wednesday afternoon.

"So the tweet fired you?" Camerota asked.

"Yes," Shulkin responded.

Shulkin told CNN's "State of the Union" on Sunday that he did not offer to resign, though a White House spokesperson insisted that he tendered his resignation.

On Monday, White House director of strategic communications Mercedes Schlapp told Fox News' "Fox & Friends" that "Kelly offered him the opportunity to resign."

"The President said it was time to move on in terms of Veterans Affairs," she added.

The distinction between whether Shulkin fired or resigned is notable because under the Federal Vacancies Act, the President can put his own candidate in place to assume a Cabinet position if the secretary resigns. Trump has installed a Defense Department official, Robert Wilkie, as acting head of VA instead of the deputy secretary, and he's nominated White House physician Ronny Jackson to become the VA's next secretary. Lawmakers and veterans' groups have raised questions about whether Jackson he has the right experience to lead the government's second largest bureaucracy.

If Shulkin was indeed fired, Trump's decision to replace him with Wilkie instead of following VA's line of succession could imperil any decisions Wilkie makes while serving at VA in an acting capacity. There could be legal challenges to any actions that Wilkie makes at a moment where VA is at a crossroads and decisions are looming about some of the department's biggest functions.

Given the lengthy process for Senate confirmation, Wilkie could serve in an interim capacity for months, until a permanent head of the VA is confirmed by the Senate.

Shulkin's firing came after an inspector general report took issue with the VA's use of taxpayer funds on Shulkin's travel. For his part, Shulkin has defended his conduct and said people who have ideological disagreements with him used the report as a "political exploit" to remove him from leadership.

Shulkin expanded on comments he made in an op-ed where he blamed political appointees for working against him in the interest of aggressively privatizing the work of the department.

"These individuals, though, when they didn't see that their way was being adopted, used subversive techniques to be able to change leadership at the VA," Shulkin said. "That's the issue that I have concerns with."