Gigi Hadid has shared a heartfelt tribute to her boyfriend Zayn Malik to mark his 25th birthday.

Zayn Malik and Gigi Hadid via Instagram (c)

Zayn Malik and Gigi Hadid via Instagram (c)

The former One Direction star turned 25 on Friday (12.01.18), and to celebrate the occasion, his model girlfriend Gigi - whom he has been romancing for over two years - posted a series of pictures of the hunk on Instagram.

And in a heartfelt caption, she wrote: "love this man more than I could ever put into words, & am inspired by his drive to be and do better everyday cheers to YOUR YEAR my @zayn - happiest happiest birthday & 25th year of life !! I'm proud to be by your side x (sic)"

Gigi's photos included a couple of snaps of the pair together, as well as two photos of Zayn with a horse.

It comes just two months after their two-year anniversary in November, when 22-year-old Gigi took to social media once again to show off a snap of the pair sharing a smooch while she held onto a glass of champagne complete with a strawberry on top.

She wrote: "2 yrs w my favorite human (sic)"

Although the pair are happy in their relationship, the 'Pillowtalk' hitmaker admitted he doesn't feel under any pressure to settle down with Gigi.

He said: "I don't think things like that should be decided based on feeling pressure. When it's the right time and place, hopefully that will happen. Who knows when that will be.

"There are a lot of people who are too busy in other people's lives. I just concentrate on my relationship and try to do right by my girlfriend and she does by me, and we hope for the best, as we all do."

But if the couple do get married in the future, they already get along with one another's families, with Gigi previously praising Zayn's mother for her cooking skills.

She said: "Zayn has helped me a lot with my British food love and Indian food love and his mum's an amazing cook. I'm trying to learn everything as I go and make a little cookbook, writing it all down instead of annoying his mum by texting her every week."