Gigi’s younger sister, fellow model Bella, posted pictures of the pair as young girls to mark the occasion yesterday.
Calling Gigi her role model and best friend, Bella, 20, wrote: “I feel so lucky every day to call you my sister.”
Former One Direction star Malik also shared a snap of himself with his girlfriend, writing: “happy birthday to my everything.”
Bella was in London last week to launch her brand new beauty campaign for Dior Pump ‘n’ Volume mascara.
She told the Standard: “Gigi has been through everything I am going through now because she has been in the business for a little bit longer than I have so to be able to get advice on things is great.”
Despite their close bond, she revealed the siblings do have their arguments. “She will completely deny it but I go to her house and she will have all of my stuff.
“Occasionally I realise it was actually me who left things behind there and feel bad for yelling at her about it but we always end up sharing clothes.”
She said dealing with the spotlight has been tough: “I like to keep people around me who have known me since I was kid."