Drinkers in the bar told how Butler was sitting by himself having a quiet drink while checking messages on his phone.
Scott Wright, a politics student at Edinburgh University, said he and friends debated whether it even was Butler sitting side on a few feet away.
Scott, 21, said: “We called the barman over and asked him and he was like ‘yeah it’s him’. So I went over and asked if it would be okay for a picture.
“He said aye it would be okay but a little later like ten minutes or so. He wasn’t dismissive or anything he was just busy doing something on his phone.
“There was like loads of writing on the screen, like an email or something. He kept reading it and was shaking his head, I don’t know what that was about.”
He added: “He had quite a heavy beard growth and was wearing a leather jacket, jeans and some Adidas trainers. He was probably trying to blend in, he’s pretty A-list.”
About ten minutes later Scott approached the bar to get a drink and made eye contact with Butler.
He offered the star one, but he politely declined.
The star then happily posed for pictures with Scott and his pals.
And when a friend’s girlfriend asked for a picture, Butler joked that he only posed for pictures with men.