Tim Phillips, the veteran Republican operative and longtime president of Americans for Prosperity (AFP), is no longer steering the powerful fiscally conservative and libertarian political advocacy group.

Phillips resigned on Wednesday after AFP made it clear he was no longer welcome at the Koch-backed organization following an internal investigation into a unspecified "personal" situation.

"While the underlying issues involved are personal in nature, Tim’s actions violate our core principles and make it impossible for him to continue in this role," AFP board chairman Mark Holden said in a statement. "This has caught us all by surprise. But we believe Tim’s departure is necessary for him, his loved ones, and for AFP."

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Phillips, in a statement Wednesday, said that "this morning, I announced my resignation as president of Americans for Prosperity in order to focus on some challenging personal matters that require my full attention." The news of Phillips’ exit from AFP was first reported by the Washington Examiner.

Phillips resigns as AFP president

Americans for Prosperity (AFP) president Tim Phillips speaks at AFP event in Salem, New Hampshire on May 14, 2021. Phillips resigned as the group's president on Dec. 1, 2021. (Fox News )

A source familiar with AFP told Fox News that Phillips had been on paid leave since just before Thanksgiving when the organization was alerted to what was described as  "personal indiscretion." The source add that AFP staff was informed of Phillips departure at an organization wide announcement on Wednesday afternoon.

A separate source familiar with the organization noted that while "the underlying issues were personal in nature, it was a matter of integrity that violated our principles."

The source emphasized that "Tim has had an important public-facing role, but all financial, strategic, and day-to-day operations have been the responsibility of the CEO or COO for the past 10 years."

Phillips, a veteran of numerous GOP presidential, statewide, and congressional campaigns, started wtih AFP in 2006. The organization was instrumental in fueling the Tea Party movement and for years Phillips has been one of the most visible players in the conservative movement. Under the director of Philips and other leaders, AFP along with its affiliated political wing Americans for Prosperity Action, have been major players in campaign politics.

Most recently Phillips quarterbacked AFP’s grassroots outreach and get out the vote efforts in his home state of Virginia on behalf of now Gov.-elect Glenn Youngkin, who last month became the first Republican in the commonwealth to win a gubernatorial election in a dozen years.

AFP was founded and financed by the Kansas based billionaire industrialists Charles and David Koch, who were known as the Koch brothers. 

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David Koch stepped away from involvement in AFP ahead of his death in 2019.