Joe Lieberman unaware of John McCain's 2008 regret until new book

Former Sen. Joe Lieberman says he was unaware Sen. John McCain regretted not selecting him as his 2008 running mate until the Arizona senator shared that sentiment in his new book and in an upcoming documentary.

“I must say, I kind of wondered, but we never talked about it. It was a classic, as close as we are,” Lieberman laughed as he spoke to ABC News. “What he said in the book meant a lot to me really because he had never said that before, and it was sort of just an expression of our friendship at a difficult time."

In his new book, "The Restless Wave: Good Times, Just Causes, Great Fights, and Other Appreciations," McCain described his regret over not adding Lieberman, a Democrat-turned-Independent, to his ticket at the urging of his advisors.

"They were giving me their best counsel. It was sound advice that I could reason for myself," McCain wrote. "But my gut told me to ignore it, and I wished I had."

Lieberman, a former Connecticut senator who served alongside McCain for 24 years, has visited his friend several times since he was diagnosed with glioblastoma last summer and calls him by phone about once a week. Lieberman said he plans to travel to Arizona this weekend to visit McCain.

Asked if there might be another reunion of the "Three Amigos," the nickname given to McCain, Lieberman and Sen. Lindsey Graham, R-S.C. in the coming months, Lieberman said, “I hope we get to go out together because it’s the three of us. It’s just an extraordinary friendship really and I consider it to be one of the blessings of my life truthfully.”

The trio reunited in Arizona last August shortly after McCain's first chemotherapy treatment following his brain cancer diagnosis.

Lieberman also weighed in on the controversy involving the White House staffer who made disparaging remarks about McCain, saying she needs to apologize publicly.

“I just think they should have apologized right away and I guess there has been a personal apology to Meghan McCain," he said. “John of all people knows, he’ll always say 'I’m far from a saint,' but so we all make mistakes and the best thing to do when you do is to acknowledge it and move on but I’m surprised that they haven’t.”