President Trump's former chief of staff Reince Priebus has officially joined the U.S. Navy.

Priebus, 47, was sworn in by Vice President Mike Pence as an ensign — the lowest ranking officer in the Navy — during a commissioning ceremony on Monday morning.

First reported by the Washington Post, Fox News confirmed in December that Priebus could be joining the military branch as a reserve officer following a recommendation from former Defense Secretary Jim Mattis.

FLASHBACK: REINCE PRIEBUS SELECTED TO JOIN NAVY AS RESERVE OFFICER

In addition to Mattis’ recommendation, a board of officers also chose Priebus as a reserve officer, the Post reported, citing defense officials and a memo.

Forty-two candidates were evaluated in December by a Navy review board, with the ex-chief of staff and four others being “professionally recommended” to join the service. Because Priebus was several years past the age limit of 42, he needed a waiver to join. He also needed to ink a deal admitting to possible career limitations, according to the report.

“Reince’s experience, education, and personality make him an ideal fit to be commissioned into the Navy Reserve,” Mattis wrote in a summer letter obtained by The Post.

Priebus served as Trump's chief of staff for roughly six months, starting at the beginning of the Trump administration in January 2017. He also served as the chairman of the Republican National Committee from 2011 to 2017.

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Priebus was congratulated by Sean Spicer, Trump's former press secretary who is a reserve officer, and other Republican politicians on Twitter.

Fox News' Matt Richardson contributed to this report.