The mother of one of the two Columbine HS teen killers is publicly speaking in detail about the massacre for the first time — and says she had “no inkling” that her son was suicidal until she read his journals.

“When I first saw copied pages of these writings, they broke my heart,” Susan Klebold writes in an essay for an upcoming issue of Oprah Winfrey’s “O” magazine.

“I’d had no inkling of the battle Dylan was waging in his mind.”

Learning that her son was at the center of the April 1999 carnage, in which he and pal Eric Harris killed 12 students and a teacher before committing suicide, “changed everything,” she says.

“For the rest of my life, I will be haunted by the horror and anguish Dylan caused,” she writes. “I cannot look at a child in a grocery store or on the street without thinking about how my son’s schoolmates spent the last moments of their lives.”

She adds that “Dylan changed everything I believed about myself, about God, about family and about love.”

In recalling that day, she notes that Dylan left their Littleton, Colo., house about 20 minutes early, leaving her confused.

“All he said was ‘Bye,’ ” she writes. “The front door slammed, and his car sped down the driveway.

“His voice had sounded sharp. I figured he was mad because he had to get up early to give someone a lift to class.”

tim.perone@nypost.com

