DENVER - Pop star Taylor Swift is expected to make an appearance in a Denver federal courtroom this week to testify in dueling civil lawsuits over whether or not she was groped by a radio host in 2013, and whether or not she got him fired for the alleged groping.

The long-simmering case comes to a boil five months after Swift said she would be taking a break from performing in 2017, telling a pre-Super Bowl concert in Houston that it would be her last concert of the year.

What's involved in this latest celebrity lawsuit:

Who is suing whom?

David Mueller, a Denver radio host, then 51, sued Swift in 2015, two years after he was fired by his station for alleged violation of the morality clause in his contract. He says he was fired two days after Swift, her mother, Andrea Swift, and manager complained he touched Swift inappropriately at pre-concert event during Swift's Red tour.

Mueller claimed in his lawsuit that he didn't touch Swift ("I am sure that I did not," he says, according to court documents), and that she and the others slandered him and pressured his employer to fire him.

Swift, then 23, countersued Mueller in 2015, alleging publicly for the first time that he intentionally groped her during a photo shoot at the event — "I've never been so sure of anything in my life," she said in a later deposition. She asserted she had nothing to do with Mueller losing his job.

What was the last major ruling in the case?

U.S. District Judge William Martinez declined in May to grant summary judgment (meaning, finding in favor of one of them without a trial) but did throw out Mueller's slander allegation.

The trial begins Monday with jury selection and is expected to last nine days. The case is in federal court because neither Swift nor Mueller live in the same state. No cameras are allowed in the courtroom, as per usual in federal courts, and security will be tight thanks to the presence of the pop superstar.

What will Swift testify about?

According to legal documents in the case, she will testify about "Mueller assaulting her by lifting her skirt and grabbing her bare bottom at her June 2, 2013, fan meet-and-greet, her reaction to Mueller's conduct, and how it affected her."

"He took his hand and put it up my dress and grabbed onto my ass cheek, and no matter how much I scooted over, it was still there," Swift says in court documents.

She will testify that she had no reason or motive to fabricate a claim that Mueller of groped her, as he and his lawyer have suggested, and that she never directed anyone to have Mueller fired.

What will Mueller testify about?

According to court documents, he will talk about the "facts and circumstances surrounding the meet-and-greet, and "the fact that he did not inappropriately touch Ms. Swift." He also will testify about the impact of losing his job and the "defamation" of his character.

Mueller, who worked for a Denver country-music station, attended the event with his girlfriend and jumped into a photo with Swift. He says Swift was cordial as he and his girlfriend left, but when he returned to the arena after going to his car, he was confronted by Swift's security guard.

Mueller argues that the guard did not react during the photo shoot and that as many as 20 other people took photographs with Swift after Mueller left.

Did Swift report the incident to police?

No. Although such an act would be a misdemeanor under local law and could lead to a possible jail sentence, Swift did not report it. Instead, she told her security guard and a photographer who witnessed the photo shoot, and discussed the matter with her mother and management team.

Swift tried to keep the situation "discreet and quiet and confidential," her lawyer, Douglas Baldridge, has argued in court.

What's a key piece of evidence?

A photograph of the encounter between the two, which has been sealed. It's also disputed: Swift's lawyers called the image "damning" proof that Mueller inappropriately touched her. Mueller argues it shows him trying to jump into the picture.

What does Swift want?

She is seeking a verdict that awards her $1, while holding Mueller responsible and "serving as an example to other women who may resist publicly reliving similar outrageous and humiliating acts," according to her lawsuit.

What does Mueller want?

He wants his name cleared, and he wants $3 million in damages. His attorney, Gabriel McFarland, has argued that someone else touched Swift and Mueller may have been misidentified.

Contributing: The Associated Press