WASHINGTON — Gary Shapley, who became a folk hero to conservatives when he revealed the Justice Department played favorites in its investigation of former first son Hunter Biden, was ousted from his role as acting IRS commissioner just days after being elevated to the position, sources familiar with the shake-up told The Post Friday.

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Treasury Secretary Scott Bessent has replaced Shapley with deputy treasury secretary Michael Faulkender following a power struggle with key Trump adviser Elon Musk over the appointment.

The reorganization was first reported by the New York Times.

Musk’s Department of Government Efficiency (DOGE) had pressed the White House for Shapley to take over the IRS.

But Bessent felt left out of the decision-making — and asked President Trump if he could install Faulkender instead.

The acting commissioner will only be in place until former GOP congressman Billy Long can be vetted and confirmed by the Senate to lead the tax collection agency.

“It’s no secret President Trump has put together a team of people who are incredibly passionate about the issues impacting our country,” White House press secretary Karoline Leavitt said in a statement.

“Disagreements are a normal part of any healthy policy process, and ultimately everyone knows they serve at the pleasure of President Trump.”

Shapley, who last month was tapped as a senior adviser to Bessent, was named acting IRS head after the departure of Melanie Krause, who resigned due to disagreements with the treasury secretary over the sharing of tax information on illegal immigrants with the Department of Homeland Security.

While Krause left the IRS on Tuesday, Shapley remains in a senior position in the commissioner’s office despite being removed from the top interim role.

Musk had been lashing out at Bessent publicly before Shapley’s apparent demotion.

On Thursday evening, the Tesla and SpaceX CEO posted on X in response to right-wing provocateur Laura Loomer that Bessent’s meetings with a purported “Trump hater” earlier this month were “troubling.”

The line of attack came after Loomer had a White House meeting that precipitated the mass firing of several National Security Council staffers due to a lack of perceived loyalty to the president’s agenda.

Musk had backed current Commerce Secretary Howard Lutnick for the Treasury role, criticizing Bessent as a “business-as-usual choice.”

Lutnick, by contrast, would “actually enact change,” Musk wrote on X before Bessent’s nomination.

Shapley and fellow IRS whistleblower Joseph Ziegler had testified before Congress in July 2023 that former President Joe Biden’s Justice Department had slow-walked a criminal probe of his son Hunter and blocked their tax team from taking certain investigatory steps.

Among the damning claims were that Biden-appointed US attorneys based in Washington DC and Los Angeles had declined to bring charges against the then-first son, while then-Assistant Delaware US Attorney Lesley Wolf discouraged investigators from pursuing lines of questioning related to Joe Biden, saying at one point that there was “no specific criminality.”

The Post has reached out to the Treasury Department and a rep for Musk for comment.