After serving 40 years in the U.S. Senate, Sen. Thad Cochran, R-Miss., announced he will resign effective April 1 because of health issues.

His decision means both Mississippi Senate seats are in play for the 2018 midterm elections.

The state’s primary is slated for June 5, but with Cochran leaving Capitol Hill early, here’s a look at what will happen to his seat.

Who will replace Cochran in the Senate?

With a vacant Senate seat, it’s up to Republican Gov. Phil Bryant to appoint a replacement within 10 days “after receiving official notices of the vacancy,” according to Mississippi election law.

While the governor doesn’t have to appoint someone in his own party, he will pick a “conservative Republican,” Clay Chandler, Bryant’s communications director, told Fox News ahead of the selection.

On March 21, he appointed Cindy Hyde-Smith, who has served as the state’s agriculture commissioner since 2011. She will be the first female member of Congress representing Mississippi.

Will there be a special election?

Hyde-Smith is expected to run in the special election, which will be held on Nov. 6, Chandler said.

The winner of that race will then serve out the remainder of Cochran’s term through January 2021, Mississippi election law dictates.

According to state law, if the Senate seat had become vacant in a year that a state or congressional election wasn’t already being held, then the governor would have to set a special election date.

Have people already announced their intention to run for the seat?

Former Rep. Mike Espy, a Democrat, has already announced his “strong intention” to run for the empty seat.

“I just learned of the pending resignation of Sen. Cochran – a person I admire and respect, and who has done so much for Mississippi over his tenure,” Espy, who also served as former President Bill Clinton’s agriculture secretary, said in a statement.

Conservative Chris McDaniel had originally intended to challenge incumbent Sen. Roger Wicker but has switched races to run for Cochran’s old seat in November’s special election.

“By announcing early, we are asking Mississippi Republicans to unite around my candidacy and avoid another contentious contest among GOP members that would only improve the Democrats’ chances of winning the open seat,” McDaniel said in a statement. “If we unite the party and consolidate our resources, we can guarantee Donald Trump will have a fighter who will stand with him.”

Fox News’ Mike Emanuel contributed to this report.