TONIGHT SHOW kingpin JOHNNY CARSON flew into a jealous rage over his wife’s alleged affair with Frank Gifford, a shocking new book by longtime confidante claims.

In his new tell-all, “Johnny Carson,” Carsons’ lawyer of 18 years Henry Bushkin writes that when Johnny Carson hired him in 1962 one of his first jobs was to chaperone Carson and a private eye to break into a Manhattan pad his wife Joanne was renting on the sly.

“I have reason to believe my wife is cheating on me,” Carson reportedly told Bushkin. “I also have an idea who the son of a bitch is that she’s shacking up with.”

Suspected lover? NFL great Gifford, who would later go on to fame  on ABC’s “Monday Night Football” and future hubby to Kathie Lee Gifford.

Allegedly, all over Joanne’s apartment were signed and framed photos of Gifford – a virtual shrine to the NY Giant,  Bushkin writes.

According to the book, Carson collpased  against the living room wall and “began to weep,” Bushkin writes. “I realized that I was probably one of the very few people who ever saw Johnny Carson cry.”

As he wailed, Carson’s raincoat fell open.  “I was shocked to see that Johnny was carrying a .38 revolver in a holster on his hip,” Bushkin writes.

Bushkin then claims that Carson then fled to a bar to drown his sorrows with boozy sidekick Ed McMahon.

According to the book, Carson lamented, “Why Frank Gifford? What’s that a- -hole got that I don’t have? That guy plays three positions on the field. I could never get Joanne to go for more than two.”

Buishkin then writes Carson quickly turned from Tragedy to Comedy, “I think I’ll use that in tomorrow’s monologue. Joanne has broken my heart to the extent I ever had one.”

Yet, Joanne, now 81, denies the story, saying she and Gifford were just good friends and promptly denouncing Bushkin’s claims as “delusional” and that his book should be classified as “fiction”.

Carson and Joanne remained married until 1972, the year “The Tonight Show” left New York for Burbank, Calif. Carson died in 2005 at age 79.