In a terse but stunning front-page announcement, the Chicago Tribune said Sunday that popular columnist Bob Greene has lost his job because of a past sexual relationship with a teenager.

“Greene’s resignation was sought after he acknowledged engaging in inappropriate sexual conduct some years ago with a girl in her late teens whom he met in connection with his newspaper column,” Editor Ann Marie Lipinksi wrote. “The acknowledgment came in response to an anonymous complaint to the Tribune last week. The complaint prompted an inquiry by Tribune editors and officials. Greene was suspended by the newspaper following initial inquiries into the allegation.”

In a statement e-mailed to the Associated Press, Greene, 55, who is married, said there have been “indiscretions in my life that I am not proud of.” Without providing specifics, he wrote: “I don’t have the words to express the sadness I feel. I am very sorry for anyone I have let down, including the readers who have for so long meant so much to me.”

The statements left all kinds of questions unanswered: How long ago did this happen? How did Greene meet the teenager? Was she over 18? Had he interviewed her for his column? But the newspaper is in no-comment mode, with spokesman Gary Weitman saying the statement “speaks for itself.”

Greene, whose column is syndicated around the country, is an author, former “Nightline” contributor, former Esquire columnist and regular commentator for Tribune’s WGN-TV. He has been a Tribune columnist for nearly a quarter-century and was a Pulitzer Prize finalist in 1998 for his writing about local children whose cases were mishandled by the welfare and judicial systems.

Greene’s visibility as something of a Chicago institution makes the abrupt nature of his ouster all the more dramatic. Lipinksi concluded her note this way: “Greene’s behavior was a serious violation of Tribune ethics and standards for its journalists. We deeply regret the conduct, its effect on the young woman and the impact this disclosure has on the trust our readers placed in Greene and this newspaper.”

Other columnists, including Mike Barnicle and Patricia Smith of the Boston Globe, have been forced out after questions were raised about their writing. But this is one of the few cases where revelations about the personal conduct of a prominent columnist have led to his downfall.

Greene has forged a personal connection with many readers by writing about his life, recently describing himself as “the uncoolest person in the world.” His four-days-a-week column has ranged from terrorism to self-adhesive stamps, from the decline of water-cooler conversation to his travels across America.

One of Greene’s books, “Good Morning Merry Sunshine,” a New York Times bestseller in 1984, is a diary of his first year as a father after his daughter’s birth. The Northwestern University graduate has also written “Hang Time: Days and Dreams With Michael Jordan,” “We Didn’t Have None of Them Fat Funky Angels on the Wall of Heartbreak Hotel, and Other Reports From America” and “Be True to Your School,” his diary of growing up in Ohio in 1964.