THE childhood of comic Stephen Colbert – who replac­es David Letterman next year – was anything but amusing.

The 49-year-old Com­edy Central funnyman – just named by CBS to succeed the veteran late-night host – had his own personal 9/11 tragedy.

On Sept. 11, 1974, when Colbert was just 10 years old, his father Dr. James Colbert, a medical school dean at Yale University, and two brothers – Peter, 15, and Paul, 18 – were killed in the crash of an Eastern Air Lines flight while it was attempting to land in Charlotte, N.C. Dad and sons were en route to enroll the two boys at school.

At the time of the horrific crash, Colbert says his entire world turned upside down.

“Things didn’t seem that important anymore,” he told an interviewer. “’Nothing seemed that important anymore.”

The “Colbert Report” host admits he didn’t truly grieve the deaths of his father and siblings until he left home at age 18.

“I didn’t really feel the loss until I was in college,” he said. “Then, I was in bad shape…I was just so sad about it.”

He revealed his weight plummeted in his freshman year from 185 to 135 pounds.

Even today he still feels grief, explaining: “It’s just as keen but not as present.”

To deal with the loss as a youngster in South Carolina, Stephen – the youngest of the family’s 11 children (seven brothers and three sisters) – curled up into the private fantasy world of the role-playing game “Dungeons & Dragons” and J.R.R. Tolkien’s “Hobbit” books.

They shielded him against the overwhelming sadness of the family tragedy.

During his late teen years, he emerged from his shell as a rock ’n’ roll pothead, playing Rolling Stones songs in a cover band.

He says he got to know people when “we waved at each other over the bong. Then I got to know people by making jokes.”

And learning that he could make people laugh proved to be a godsend.

“The most tragic event in Stephen’s life made him the comedian he is today,” a friend of the funnyman told The ENQUIRER. “Humor was his outlet. It saved him.”

Stephen pored through all of his dead brothers’ comedy albums, including comic Bill Cosby’s classic “Wonderfulness,” which he memorized from start to finish.

He attended Northwestern University and joined Chicago’s famed Second City improvisational group.

A series of successful TV comedy jobs then came along and made him a star. There was the cult favor­ite “Strangers with Candy.” He also was the comical correspondent on Jon Stewart’s “The Daily Show,” and finally got his own wildly successful “Colbert Report” (which debuted in 2005). On the show he plays himself but as a witless conservative commen­tator, whose mistakes show how right liberals are. The show’s wild success led to his selection as Let­terman’s replacement.

While Letterman has a reputation as a quirky, edgy host, viewers will soon discover that Colbert also has quirks – for instance, he has a fear of bears.

In an appearance at Harvard University, he re­vealed that his on-air character’s fear of bears was in part inspired by a recurring nightmare he had, in which a bear is standing between him and a goal.

“I don’t dislike bears, but I am kind of afraid of them,” he confided to an interviewer. “There was a time when, if I had dreams about bears, something bad was going on in my life.”

Probably the worst thing that happened to him on-air was a shocking physical injury.

On June 27, 2007, the lean, athletic star broke his left wrist on the set while performing his warm-up for the show. But he turned even that disaster into a funny bit. Colbert launched a tongue-in-cheek cam­paign against Hollywood’s supposed glorification of “wrist violence.”

In real life, the funnyman is very much a family man.

He has been happily married for 20 years to Evelyn McGee, who appeared with him in an episode of “Strangers with Candy” – as his mother!

Together they have three children – Madeleine, Peter and John – and live in Montclair, N.J.

The future is bright for the versatile comedian. He is already worth an estimated $45 million, but stands to make far more from his five-year deal to take over the “Late Show.”