President Donald Trump will nominate former Boeing executive Patrick Shanahan to the top Pentagon post, White House press secretary Sarah Sanders said in a statement Thursday.

"Shanahan has proven over the last several months that he is beyond qualified to lead the Department of Defense, and he will continue to do an excellent job," Sanders said, according to The Associated Press.

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The Washington Post reported that Shanahan said in a statement that he was honored by the nomination.

“If confirmed by the Senate, I will continue the aggressive implementation of our National Defense Strategy,” he said. “I remain committed to modernizing the force so our remarkable Soldiers, Sailors, Airmen, and Marines have everything they need to keep our military lethal and our country safe.”

Related: Who is Patrick Shanahan, ex-Boeing executive and Trump's nomination for secretary of defense?

In December, Trump named Shanahan acting secretary of defense. Shanahan started the role Jan. 1.

"I am pleased to announce that our very talented Deputy Secretary of Defense, Patrick Shanahan, will assume the title of Acting Secretary of Defense starting January 1, 2019," Trump tweeted Sunday morning. "Patrick has a long list of accomplishments while serving as Deputy, & previously Boeing. He will be great!"

The announcement came days after Secretary of Defense Gen. James Mattis announced he was resigning.

Although Trump said Mattis was "retiring with distinction at the end of February," Mattis said himself in a letter to Trump that he was resigning. Mattis cited differences in foreign policy issues and national security as the reason for his exit.

Related: Jamie Dupree: At odds with Trump over Syria withdrawal, Mattis quits as defense secretary

“Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position,” Mattis said.

FILE - In this April 9, 2018, file photo, Deputy Secretary of Defense Patrick Shanahan, right, listen as President Donald Trump speaks during a cabinet meeting at the White House, in Washington. A U.S. administration official says that Defense Secretary Jim Mattis will leave his post Jan. 1, 2019, as Trump is expected to name Shanahan as acting secretary.

Credit: AP Photo/Evan Vucci

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Credit: AP Photo/Evan Vucci

Trump’s Twitter announcement means Mattis will be leaving more than a month before his initial end date of Feb. 28.

Shanahan was previously a Boeing executive before becoming the 33rd deputy secretary of defense on July 19, 2017. He spent more than 30 years with the aircraft manufacturing company.