On Monday, Braun told the Diary of a CEO podcast: "When I bought Big Machine, I thought I was going to work with all the artists on Big Machine. I thought it was going to be an exciting thing."
He had previously met Swift three or four times, including one occasion when she "invited me to a private party and we respected each other", he said.
"In between that time, since I'd seen her last, I started managing Kanye West, I managed Justin Bieber. I knew she didn't get along with them."
Braun said he thought there might be an issue given Swift's history with West and Bieber.
West famously stole Swift's thunder at the 2009 MTV Awards by coming on stage during her acceptance speech. Rumours about Swift and Bieber not getting on have circulated for years, and began before Braun's company bought her master recordings.
Braun, who is now retired from talent management, explained: "I had a feeling - this is where my arrogance came in - I had a feeling she probably didn't like me because I managed them. But I thought that once this announcement happened, she would talk to me, see who I am, and we would work together."
He said he spoke to other artists signed to Big Machine, who were "excited", and was set to call Swift too.
"And then this Tumblr [post] comes out and says all this stuff. And I was just, like, shocked."