Karisma posted a picture on Instagram the read "It's a baby boy that makes me a proud maasi!".
She captioned the photo with various hashtags including the little one's name Taimur Ali Khan Pataudi.
Kareena's best friend Amirta Arora welcomed her to the "mommy club".
"My darling welcome to the best club everrrrr....'Mommy club'....Love u#whenthebabybecomesamomma," she captioned a picture of Kareena and Saif.
Malaika Arora Khan, who is also part of the girl gang, shared Amirta's post.
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"The family is delighted. Taimur Ali Khan Pataudi is a beautiful baby boy and both mother and son are doing very well!!," Soha told PTI.
The 36-year-old actress' close friend, filmmaker Karan Johar, wished the couple on Twitter.
"My Bebo had a baby boy!!!!!!! Am so so happy!!!!!!! #TaimurAliKhan," Karan tweeted.
Kareena's "Veere Di Wedding" co-star and friend Sonam Kapoor welcomed the "mini nawab".
"Congratulations my darling Bebo and Saif! #taimuralikhanpataudi is going to be the apple of everyone's eye... #mininawab," she wrote.