New Jersey Gov. Chris Christie (R) on Thursday announced he will appoint state Attorney General Jeff Chiesa to the seat left vacant by the death of Sen. Frank Lautenberg (D-N.J.).

Chiesa will serve for only a few months, until a new senator can be elected in a special election. Christie on Tuesday set the special election for Oct. 16.

Christie said he will file the paperwork and Chiesa (pronounced Key-AY-zuh) will be sworn in Monday.

Chiesa’s name came largely as a surprise. In the hours before his selection, many thought Christie would pick another former New Jersey attorney general, David Samson.

Chiesa is a longtime Christie ally, having served with him during his time as U.S. attorney and heading his transition team when he won the 2009 governor’s race.

He was appointed attorney general in January 2012. (The office is an appointed position in New Jersey, though in most states, attorneys general are elected.)

Chiesa confirmed he will not seek the seat in the looming special election. He said he is a registered as a Republican and that he believes he registered as such in 2000.

Speaking alongside Christie, Chiesa described himself as a "conservative Republican." Asked about his position on immigration -- one of they key issues he will likely vote on -- Chiesa said he is a border-security-first Republican.

“I think the first thing we have to do is make sure the borders are secure," he said. "From there, these issues are new to me.”

Christie said Chiesa's selection should hearten members of both parties.

"There are very few people in my life that I know better than Jeff," Christie said, adding: "You won’t find anybody, I think, who will have something bad to say about Jeff:"

Christie and Chiesa attended the press conference at the same time that Lautenberg's body was being brought into the U.S. Capitol following Wednesday's funeral.

Updated at 2:02 p.m.