(CNN) President Donald Trump's former chief physician, Rear Admiral Ronny Jackson, retired from the Navy on Sunday even as the Defense Department's Inspector General continues to investigate allegations that he was periodically intoxicated and mishandled prescription drugs, CNN has learned.

Former Navy Secretary Richard Spencer approved Jackson's retirement before his ouster, according to a senior DOD official. Jackson did not respond to a request for comment.

Typically military officials under inspector general investigation are not allowed to retire until the probe is completed. However, there are provisions for personnel to retire while under investigation under the condition they might be brought back on active duty to face disciplinary action if wrongdoing is found in administrative matters such as the allegations facing Jackson.

In that case, standard military procedures would allow for Jackson to be brought back on active duty and face a reprimand or even a reduction of rank in his retirement, which could impact his pension -- though Trump could also overturn any potential disciplinary action.

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