John McCain is in "good spirits" and "cracking jokes" with his nurses as he battles a life-threatening form of brain cancer, said Mark Salter, the co-author of the Arizona senator's newest book.

"He's doing well he got out of the hospital a couple of weeks ago after an operation and he's working really hard at getting strong," Salter said Monday in an interview on "CBS This Morning."

Salter, who visited McCain at his house near Sedona a week ago, is a longtime aide who has written several books with the 2008 Republican nominee for president, including his latest, "The Restless Wave: Good Times, Just Causes, Great Fights and Other Appreciations."

[WATCH: Mark Salter on "CBS Thi Morning"]

[SPECIAL SECTION: John McCain Stories]

During the CBS interview, Salter revealed the forthcoming book started with a different title but McCain changed his mind because he thought it was "too flip."

"It actually had a different title; those of you who covered him will be familiar with it," Salter said. "It was 'It's Always Darkest Before It's Totally Black.'"

[READ MORE: McCain penning 'no-holds-barred' memoir]

The expression is one of many used throughout the years by McCain, who is known for his self-deprecating humor and sarcasm.

Regarding that sense of humor, Salter said McCain's nurses are still adjusting to his personality.

"Some of them are really new. They don't really know him so they don't understand that sarcasm is his form of affection," Salter said.

The book goes on sale Tuesday and was already in the works when doctors diagnosed McCain with brain cancer nearly a year ago. Salter said the diagnoses changed the focus.

[READ MORE: Sen. John McCain diagnosed with brain cancer]

"It became a different book," he said. "Obviously, he wanted it to be very personal at that point and write about what America means to him after 60 years of serving the country."Click/tap here to download the free azfamily mobile app.Copyright 2018 KPHO/KTVK (KPHO Broadcasting Corporation). All rights reserved.

Political Editor

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