The 27-year-old singer took to the witness stand in a court in Denver, Colorado, on Thursday (10.08.17) over claims Mr Mueller groped her during a meet-and-greet session after a gig at the Pepsi Center in June 2013.
Responding to Swift's appearance in court, the 'Girls' creator wrote: ''Proud of @taylorswift13 for her fierce & cutting testimony & her refusal to settle for being treated like property. Her example is powerful (sic)''
During her testimony, Taylor told the court that the alleged assault was ''despicable and horrifying''.
Recalling the incident, she explained to the jurors: ''He stayed attached to my bare a** cheek as I lurched away from him.
''It was a definite grab. A very long grab.''
Mr Mueller lost his job at the KYGO radio station following the accusation and subsequently launched a $3 million lawsuit.
During her appearance in court, Swift was asked by Mr Mueller's attorney Gabriel McFarland whether the DJ got ''what he deserved'' and she responded: ''I don't feel anything about Mueller. I don't know him.
''I think what he did was despicable and horrifying and shocking.''
Swift also explained why her bodyguard at the time, Greg Dent, did not see the alleged assault.
She said: ''He saw your client lift my skirt, that's when your clients hand went out of his view because it was grabbed onto my a** cheek.''
The singer added that the only way someone could have seen the alleged incident was if they were ''lying directly under my skirt and we didn't have anyone positioned there''.
Swift - who is counter-suing Mr Mueller for the symbolic sum of $1 - added: ''What Mr Mueller did, like I said, was very intentional and the location was very intentional, and it happened very quickly. I wasn't going to blame Greg Dent for something Mr Mueller did.
''None of us expected this to happen - it had never happened before.''
Mr Mueller has denied the allegation.
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