During the heart of the bitter jousting over the fate of "The Tonight Show," soon-to-be-ousted host Conan O'Brien delivered perhaps the best joke of the whole affair:

"Hosting 'The Tonight Show' has been the fulfillment of a lifelong dream for me. And I just want to say to the kids out there watching: You can do anything you want in life. Yeah." O'Brien paused. "Unless Jay Leno wants to do it, too."

The joke, back in January, stung because it played right into the narrative of O'Brien's supporters: Leno, the former "Tonight Show" host, wasn't willing, after all, to cede the job he had given to O'Brien.

But it also was the end of NBC's hopes to keep both O'Brien and Leno at the network, New York Times writer Bill Carter claims in his new book, "The War for Late Night."

"Until that joke was told, NBC still thought, maybe there's a chance to keep this thing together," Carter said Sunday on CNN's "Reliable Sources."

"And after that, Jay called and said, 'I can't work with this guy. This is never gonna work out.'"

The book is a sequel of sorts to Carter's "The Late Shift," which became the book of record about the last fight over "The Tonight Show," between Leno and David Letterman back in 1992.

And it presents all the key players in a different light — complicating the O'Brien fans' portrayal of Leno as a scheming bad guy.

Leno, Carter stresses, always wanted to avoid burning bridges.

It also elicits sympathy for Jeff Gaspin, the chairman of NBC Universal TV Entertainment who on Monday announced his departure from the network.

Carter writes in an excerpt of the book in Vanity Fair that Gaspin was the one who developed and tried to orchestrate the compromise in which Leno would move from the 10 p.m. slot, where he was floundering, back to 11:35 — and O'Brien's "Tonight Show" would move to midnight.

Gaspin's departure Monday highlighted just how unpredictable the late-night landscape has proven to be for everyone involved.

Who could have guessed, back when NBC decided to cancel Leno's show at 10, that of Leno, O'Brien, and Gaspin, only Leno would remain an employee of NBC?