US President Donald Trump appointed current Department of Homeland Secretary General John Kelly as the new White House Chief of Staff on Friday, replacing Reince Priebus.

“John has done a spectacular job at Homeland Security. He has been a true star of my administration,” Trump said.

The US President made his announcement first on Twitter, praising the former Marine Corp general as a “Great American” and “Great leader” in a series of tweets.

Spanning four decades in the military service, the former four-star general is the highest-ranking military officer to lose his child in the wars in Iraq and Afghanistan. In his job at Homeland Security, he was responsible for border, immigration, cyber hacking, airport security and natural disaster management

On Thursday, Priebus resigned as Chief of Staff after talking with Trump. The former White House official was also accused of leaking to the press.

“The president wanted to go in a different direction,” Priebus told CNN’s Wolf Blitzer, adding that he thought Kelly was “a brilliant pick.”

Kelly, according to a White House spokesperson, will start working on Monday.

Meanwhile, Kelly’s deputy, Elaine Duke, will temporarily spearhead the Department of Homeland Security.