"I went into the dressing room and I saw her face," Andrea Swift told jurors in Denver. "I could see that there was something horribly wrong.

"She said, 'Mom, a guy just grabbed my ass,'" she continued. "I wanted to vomit and cry at the same time."

Swift is suing radio DJ David Mueller over the incident, which he denies.

The alleged assault occurred in 2013, during a Denver stopover on Taylor Swift's Red tour.

Mueller, then a host on the top-rated radio station KYGO, had been invited to meet the star before the show. As they posed for a photo, Swift claims, "he put his hand under my dress and grabbed my bare ass".

Recalling the night, Andrea Swift said her daughter expressed bewilderment that she had "thanked" Mueller and his then-girlfriend after the incident.

"It was just destroying her that she said that," she testified. "As a parent it made me question why I taught her to be so polite."

Wiping away tears, she added: "She was really shaken. She was humiliated."

Andrea Swift, who is part of the star's management team, said she did not report the incident to police because: "I did not want this event to define her life."

"I did not want her to have to life through the endless memes and gifs that tabloid media and internet trolls decided to come up with - doctoring the pictures… and making her relive this awful moment over and over again."

Asked whether she had sought witnesses, Ms Swift - who was not present at the encounter - she said she had no reason to doubt her daughter.

"He sexually assaulted my daughter," claimed Andrea Swift in court, pointing her finger at the broadcaster. "Right there, that guy,"

"I heard it from my daughter's mouth. I know that it happened."

Two days after the concert, Mueller lost his $150,000-a-year job at KYGO, after Swift's radio liaison [radio representative] Frank Bell alerted the station to the alleged assault.

Taking the stand on Wednesday, Bell said he asked the broadcaster to investigate the encounter but had not requested that Mueller be fired.

Following his dismissal, Mueller sued Swift for defamation, seeking $3m (£2.3 million) in damages.

An eight-member jury, comprised of six women and two men, is weighing both claims in a single trial at the US District Court in Denver.

'Trust shattered'

Testimony began on Tuesday and is expected to last nine days. Mueller was the first to take the stand, describing his encounter with Swift as "weird and awkward".

"I know my hand was touching her rib or her skirt," he testified. "And it went behind her, and her hand, or arm, went behind my arm."

Asked by his own lawyer whether he had grabbed Swift's bottom, Mueller said flatly, "No, I did not."

Concluding his testimony on Wednesday, he said: "I'm here to prove that I'm innocent. I had a good reputation in radio and I would like to get it back."

Swift's mother said the incident had "absolutely shattered our trust", and that the star now took many more precautions when meeting fans.

"Our meet-and-greets are much smaller," she said. "We now have metal detectors. We wand people. We now do background checks. It scared us really badly."

The pop star, whose hits include Shake It Off, Love Story and I Knew You Were Trouble, has been present for every day of the trial.

She listened closely and took notes during Mueller's testimony; and is expected to take the stand herself in the coming days.