The 38-year-old shared the happy news about their son's birth with fans on Friday morning, reports dailymail.co.uk.
The couple are already parents to daughter North, 5, son Saint, 3, and daughter Chicago, 15 months.
"He's here and he's perfect,' Kim tweeted. Minutes later she added: "He's also Chicago's twin. Lol. I'm sure he will change a lot but now he looks just like her."
The baby was born on Thursday evening, according to TMZ.
This comes after Kim's sister Kourtney, 40, surprised their mother Kris, 63, with the news that the surrogate was in labour with the child during an appearance on "The Ellen Show" on Thursday.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)