Taylor Swift has told a court a former radio DJ reached under her skirt and intentionally grabbed her bottom during a meet-and-greet photo session before a 2013 concert in Denver.
"He stayed attached to my bare ass-cheek as I lurched away from him," the pop star said in federal court in Denver during a trial over the claim.
Despite being stunned, Swift said she did not say anything to David Mueller about it because she did not want other fans lined up to hear anything and she did not want to cancel the event and disappoint them.
Swift said she tried to get as far away from Mueller as she could.
The singer said she told Mueller and his girlfriend, Shannon Melcher, who was also in the photo, "thank you for coming" in a monotone voice before they left.
Mueller sued Swift and others on her team, claiming they cost him his job, and is seeking up to three million dollars (£2.3 million) in damages.
The pop star counter-sued, alleging sexual assault, and is asking for a symbolic one dollar judgment.
Swift said a security guard working for her witnessed the groping.
She said that guard Greg Dent saw Mueller "lift my skirt" and grab her but that it was impossible for anyone to see Mueller's hand beneath her skirt and on her buttock because they were posing for the photo with their backs to a wall.
Swift said that someone would have had to have been underneath her to see the actual groping "and we didn't have anyone positioned there".
Mueller told the court on Wednesday that the photo taken before the concert was "weird and awkward", but he insisted that he touched Swift in the ribs, not on the bottom.
He said his hand was touching Swift's skirt after he put his arm around her and their arms got crossed, adding: "My hand was at rib-cage level and apparently it went down."
The case is being tried in federal court under a law allowing the proceeding when the parties live in separate states and the dispute involves a damages claim higher than 75,000 dollars (£58,000).