"The Bruce I saw was isolated, was lonely, was lost," Bissinger told ET. "There was a connection missing. There's now a connection. There's a reaching out. There's empathy. There's reaching out to his kids. He was a great father to the Kardashians, and wants to be a good father to the Jenner side."
The Pulitzer Prize-winning author penned the much talked-about profile on Caitlyn in Vanity Fair's July 2015 issue and was also present for the emotional photo shoot.
"Casey came to the shoot, and there was a moment when Casey sat next to [Caitlyn] on the couch," recalled Bissinger, referring to Caitlyn's daughter from her first marriage to Chrystie Jenner. "It was this perfect moment of a father with her daughter and daughter with her father -- you could see the possibility of connection."
Bissinger said that Casey has had a strained relationship with Caitlyn at times. Most recently, they've disagreed over a docuseries that Caitlyn is doing.
"[Caitlyn] really wanted the participation of the kids," Bissinger said. "The kids, to their credit, said, 'No, we are really worried this is going to turn into a spectacle. Dad, you have the possibility of ensuring a legacy for yourself along the lines of Muhammad Ali -- an athlete who truly engineered social change.' They could've had financial gain and exposure. They said no. She didn't like hearing that. She was upset. It's a work in progress. I think both are reaching out. It's not going to happen overnight."
Much has been said about Kris Jenner throughout Caitlyn's transition, but Bissinger said that he found her to be open and honest.
"I detected anger only in the sense of hurt," Bissinger said. "I think Kris feels, 'Why didn't you just tell me that at the beginning and let me make my own decision?' On the other hand, I think Kris felt, 'I can fix this. I'm a great wife,' and I think Bruce felt, 'This is going to go away.'"
Watch the video below to see the overwhelming support Jenner has received for her incredible Vanity Fair cover.