"It's a boy, I think it's been out there," the mother of three added. "I got drunk at our Christmas Eve party and told some people. I can't remember who I told because I never get drunk."
She said the baby was due "sometime soon".
The new bub, reportedly due in May, joins daughter Chicago, who was born last January via surrogate, daughter North, 5, and their first son, three-year-old Saint.
The episode aired on the eve of baby Chicago's first birthday. Kim posted a sweet message to her youngest child on Instagram.
"Happy Birthday to my pretty girl Chi!!!! The sweetest baby in the whole world! Mommy and Daddy love you so much!" she wrote alongside a black and white photo of the smiling youngster.
The Keeping Up With The Kardashians star has been open about her struggles with pregnancy and decision to use a surrogate, as she had previously suffered from placenta accreta — a serious condition where the placenta becomes too deeply attached to the wall of the uterus.
