Karan and Anup took to twitter to wish the legend.
"Gulzar Saab's janamdin today... 'Mera kuch samaan" from 'Ijazat' is a song I will thank him for... for the rest of my life," tweeted Karan.
Anup wrote: "Happy birthday Gulzar sir. Miss travelling with you sir for our play 'Kharashein..."
Gulzar, whose real name is Sampooran Singh Kalra, started his career as a lyricist with the hit song "Mera gora ang lai le" in "Bandini" and went on to pen dozens of chartbusters including "Tere bina zindagi se", "Aanewala pal jaane wala hai", "Mera kuchh saamaan" and "Tujhse naraaz nahin zindagi" as well as peppy numbers like "Kajra re", "Beedi" and "Darling".
If he proved his mettle as a lyricist, the National Award-winner churned out some of the best remembered movies when he went behind the camera to direct "Koshish", "Parichay", "Aandhi" and "Maachis", to name a few.
Gulzar was married to actress Raakhee, but later they separated. They have a daughter Meghna, who directed films like "Filhaal" and "Just Married".
He also published poetry books and was awarded Padma Bhushan.