Zayn Malik's "life changed forever" when he became a dad

In a special Instagram tribute to mark Khai's fourth birthday, Zayn wrote: "Happy birthday to the most important person in my life, I love you more than words allow me to express, beyond proud to call you my daughter.. grateful for every second I get to spend next to you, as you become the incredible person I know you already are. Four years ago today my life changed forever and I wouldn't be the man I am today without you."

Zayn also posted a picture of himself and Khai on a beach to accompany the sweet message.

Meanwhile, Gigi, 29, hailed their daughter as an "angel" on the youngster's fourth birthday.

The model marked the tot's big day by posting a tribute video for the girl on her Instagram Stories.

She wrote over the post, which contained a clip of Khai playing on a swing set at a park - without showing the girl's face: "4 years of YOU. Happy birthday mama's Angel!"

Gigi also included a photo of her daughter's rainbow birthday cake, adding in a caption: "Cake 4 bday breakfast always."

Earlier this year, Zayn revealed he and Khai love watching cartoons together.

He told NYLON: "I actually cried at a cartoon, I don't know if it's familiar with people. It's called Bluey. It's for kids. It makes me cry regularly. I don't know why."