Pop star Taylor Swift took the witness stand Thursday to argue her side of the story against a former Denver DJ who she says groped her during a meet-and-greet in June 2013.

Swift was the first person called to take the stand during the third day in what’s expected to be a nine-day trial at Alfred A. Arraj United States courthouse in downtown Denver.

But before Swift could testify, the judge’s first order of business was to announce that Taylor’s mom, Andrea Swift, was not feeling well and had been granted leave from court proceedings for the day.

During her nearly hour-long testimony, Swift was insistent on her position that former KYGO radio host David Mueller “grabbed her bare ass,” during a meet-and-greet on June 2, 2013.

“He grabbed outside of my clothing, he grabbed my ass underneath my clothing. And refused to let go,” Swift said. “It was a definite grab, a very long grab.”

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When questioned about how long the alleged grab lasted, Swift says she wasn’t comfortable estimating that in court, but that it was long enough to for her to be completely sure it was intentional.

“The first couple of milliseconds I thought it must be a mistake so I moved to the side very quickly so his hand would be released from my ass cheek,” Swift said. “It was a very shocking thing that has never happened to me before."

After the alleged incident, Swift said she couldn’t make eye contact with either Mueller, or his girlfriend at the time, Shannon Melcher, but said to them in a monotone voice, “thanks for coming.”

All three were captured in a photo at the event, which was later leaked to TMZ. Discussion on exactly what that photo showed took center stage during court on Wednesday.

Mueller says this allegedly false accusation got him fired from a $150,000 a year job and prevented him from finding radio work since.

He sued the 10-time Grammy winner two years after the incident – but says he’s not asking for the $3 million advised by a damages expert. Instead, he’s seeking whatever the jury sees fit.

Swift countersued for battery and assault. Her mother told the court that since the incident at the Pepsi Center, the star has changed how she interacts with fans.

Why didn’t Swift report the alleged groping immediately?

When pressed about why she didn’t report the incident right after it happened, Swift told the court she didn’t want to ruin the experience of the couple dozen fans who were still waiting in line.

“I couldn’t have [reported it] without the fans inside the booth overhearing, she said.

Swift also answered questions related to her body guard at the time, Gregory Dent – like why he didn’t take action after noticing Swift was uncomfortable following her interaction with Mueller.

Swift argued that Dent was unable to see what had happened based on his positioning in the room where the meet-and greet took place, and that he was focused on the fans entering the photo booth.

Swift also said her and Dent did not have a signal for those kinds of things because they had never needed one in the past.

Swift’s assistant: ‘She looked uncomfortable”

Swift’s personal assistant at the time, Gabrielle Liddicoat, shared what she remembered about the 2013 incident during a testimony on Thursday.

Liddicoat was in attendance for all the meet-and-greets on June 2, 2013, and recalls Swift briefly talking with Mueller before the photo – though she doesn’t know what was discussed.

Swift had said earlier in the day that Mueller was adamant she knew he was a radio DJ, and that their interaction was “filled with expectation to how I’d react to that information.”

“I saw her lean in on one side and she looked uncomfortable, but didn’t indicate anything was wrong at the time,” Liddicoat said.

Liddicoat remembers Swift being “visibly upset” once all fans had left the photo booth room, but it wasn’t until after the event, while walking back to Swift’s dressing room, that Liddicoat was made aware of what allegedly happened.

Mueller’s former bosses weigh in on ‘the photo’

Two of David Mueller’s former bosses at KYGO – Bob Call and Eddie Haskell – offered some insight into what happened in the days after the incident during testimonies on Thursday afternoon.

Shortly after Frank Bell, a member of Swift’s manager team, contacted KYGO about the incident, Call held a 45 minute long meeting with Haskell, Mueller’s direct supervisor.

At that time, Haskell described the photo as “damning,” and Call said that the photo showed Mueller’s hand, without question, behind Swift’s rear end.

Haskell admitted he participated in efforts toward getting Mueller fired, but that it was ultimately Bob Call’s decision to make.

Call told the court he thought Mueller was lying about his interaction with Taylor Swift and that’s why he fired him under the morality clause of his contract with KYGO.

Behind the scenes of the meet-and-greet

Taylor Swift’s road manager Erica Worden, estimates that about 70 people were at the meet-and-greet the night of the alleged incident.

Worden, who has worked for Swift in some fashion since 2009, remembers the moment where Swift told the entire room “that guy touched my butt” following a photo taken for a meet-and-greet.

Swift's photographer, Stephanie Simbeck, took the photo capturing the alleged grab, and told the court late Thursday afternoon she had “no doubt” that Mueller touched Swift’s butt while posing for the photo.

Court is expected to resume Friday morning at 8:45 a.m. At that time, the counsel may begin discussing a timeline for closing arguments.