The pair welcomed the baby via surrogate and he joins sisters North, 5 and Chicago 1, and brother Saint, 3.
On “The Ellen Show” Thursday with her nieces and nephews, Kourtney Kardashian said her sister was supposed to join her but couldn’t because the surrogate was in labor.
Their mother and family matriarch, Kris Jenner, appeared surprised and said she was not aware labor had started.
The baby’s name is sure to be of interest.
In January, Kardashian West said she had been Googling Armenian boys’ names in honor of her family’s heritage but had not found anything.