She also said the baby looks like 1-year-old daughter Chicago's "twin."
"My mom doesn't even know this, but Kim's surrogate went into labor!" she told the talk show host.
RadarOnline.com reported in January the star and hubby would be welcoming their fourth child.
An insider told Us Weekly the superstar couple had one male embryo left, and a surrogate was expecting the newest addition to their family “in very early May.”
A second source said Kardashian, 38, “always wanted four kids.”
But during last season of Keeping Up With the Kardashians, Kim revealed her rapper hubby wants seven kids!
The celebs are also parents to daughter North, 5, and son Saint, 3.
Despite their growing family, Kardashian has grown frustrated in her marriage with West — even thinking divorce could be her “only option,” a source previously told RadarOnline.com.
“Kanye continues to throw Kim and her family into the fire and she is constantly getting threats and harassment,” the source said. “It is just past the point of getting old, and Kim is so fed up with all of this.”