Taylor Swift's bodyguard has testified in the singer's ongoing assault and battery trial, revealing he witnessed a radio presenter grope his boss' butt.

Greg Dent took the stand in Denver, Colorado on Friday (11Aug17) and told the court he witnessed local DJ David Mueller's inappropriate act, which cost the radio host his job.

"I didn't do anything because sometimes she (Taylor) said I was a little too mean...," the minder said. "I can't tell you how long his hand was there. I just can tell you he put his hand under her skirt, she pushed it down."

Dent also revealed the singer didn't seem to be bothered by the butt grab at the time - and so he thought it was no big deal: "I take my cues from her and she continued with the photo."

On Thursday (10Aug17), Taylor herself testified and revealed politeness and professionalism stopped her from making a fuss after she allegedly felt Mueller's hand on her backside.

"It was a definite grab, (a) very long grab," ​the pop star said. "It was long enough for me to be completely sure it was intentional. He stayed on my bare cheek as I lurched away from him uncomfortably.

"The first couple of milliseconds, I thought it must be a mistake. I moved to the side very quickly... It was a very shocking thing that I have never dealt with before… It was underneath my skirt."

"After this happened, a light switched off in my personality," she added. "I just said, in a monotone voice, 'Thank you for coming', and then they were gone."

Mueller sued Swift in 2015, claiming she'd falsely accused him of groping her and cost him his job. Swift, who is only seeking $1 in damages, counter​-​sued for assault and battery.

Mueller's former KYGO co-host Ryan Kliesch and his ex-girlfriend Shannon Melcher, who was also pictured in the meet and greet photo with Swift also took the stand on Friday.

Melcher testified that "the photo happened very quickly" and she wasn't paying attention to what her then-boyfriend was doing.

The case continues.