Kim Kardashian West has wished son Saint a happy birthday with a touching Instagram post.

The reality TV star and cosmetics entrepreneur said the four-year-old brings “so much joy into my soul”.

Alongside a picture of a smiling Saint and his curly hair, she wrote: “I have no words to describe how much I love your smile and those curls of yours Saint! You bring so much joy into my soul.

“You are so kind, loving and just so thoughtful and sweet! I am so happy today if your 4th birthday and We get to celebrate how much you’ve grown! Happy birthday my sweet sweet Sainty.”

Kardashian West, who is also mother to North, six, Chicago, one, and seven-month-old Psalm with husband Kanye West, then revealed a sweet routine between her and Saint.

She said: “(When I say to him my sweet sweet Sainty, he says back to me my sweet sweet sweet sweet Momma, the best momma in the world and the only momma I ever want! HOW CAN YOU NOT MELT AT HIS SWEETNESS).”

Kardashian West’s mother, Kris Jenner, also wished Saint a happy birthday.

Alongside a set of pictures of Saint, she said: “I can hardly believe you are 4 years old!!!! You are growing up so fast… you are such a sweet, funny, kind and amazing boy and I love seeing your sweet face and beautiful smile.

“You bring such joy to everyone around you!! I love you Sainty!!!!”