Jayden, the third child he had with now-ex Liza Morales, was born on December 15, 2005, but was taken by cot death on June 29, 2006.
Years before he met and married Khloe Kardashian, Lamar suffered the devastating tragedy.
The basketball player, who also shares Destiny, 22, and Lamar Jr, 18, with Liza, detailed his heartbreak in his memoir Darkness To Light.
And he explains why he didn’t even cry until three years later.
Liza’s mother had moved in with her and Lamar to help care for their three young children.
Lamar writes that on the morning of June 29, Liza woke and went into Jayden’s room to check on him.
She found him lying still on his stomach, with his blankets undisturbed from the night before.
She thought it was unusual that he was lying on his stomach, but he looked comfortable and she didn’t want to disturb him so went downstairs and joined her mother in the kitchen.
But as soon as Liza’s mother asked how Jayden was, she began to panic and ran straight back up to his room.
Lamar writes: “His face was a dark blue. He wasn’t breathing. Liza screamed hysterically. Liza’s mother, a registered nurse, immediately took Jayden.”
Liza frantically called 911 and an ambulance and fire trucks were dispatched within minutes.
Jayden was taken away in an ambulance.
Lamar was away in Manhattan at the time and Liza called him to tell him that something had happened to Jayden.
He couldn’t comprehend what she was saying, and thought something had happened to LJ, his eldest son Lamar Jr.
He got dressed and headed for the hospital.
Lamar was ushered to a private room where Liza was wrapped in a hospital blanket. All they knew was that doctors were running tests on their son.
He writes: “Fifteen minutes after I got there, a doctor entered the room and grasped Liza’s hand. There were tears in the doctor’s eyes.
“‘I’m sorry’, she said. ‘As a mother I’ve experienced crib death, too’.
“Crib death. That was the first time I had ever heard that term. I didn’t know what it was. Jayden had died from sudden infant death syndrome.”
Lamar said it took him a long time to come to terms with the awful events.
He added: “It just didn’t make sense to us. How could our baby just die in his crib? This couldn’t be a real thing. I was stunned, numb, almost emotionless. I couldn’t move.
“I did not cry then. Or the next day. I did not cry for Jayden for three years. I thought if I cried it would make it real. I did not cry so that he might live.”