(CNN) A surrogate for Kim Kardashian and Kanye West has gone into labor with the couple's fourth child, their publicist said late Thursday night.

West and Kardashian are expecting a boy. During an appearance on "The Ellen Show" earlier in the day with her nieces and nephews, Kourtney Kardashian said her sister was supposed to be on the show, but could not make it because the surrogate was in labor.

Their mother and family matriarch, Kris Jenner, appeared surprised and said she was not aware that her daughter's surrogate had gone into labor.

I surprised @KrisJenner with 6 of her grandchildren. Then I surprised her with one more. Sending love to you, @KimKardashian and @KanyeWest! @kourtneykardash pic.twitter.com/7SzHA2sahM — Ellen DeGeneres (@TheEllenShow) May 10, 2019

In January, the TV reality star-turned-mogul said she has been Googling Armenian boys' names in honor of her family's heritage but hasn't found anything.

Her other children are named North, Saint and Chicago.