Gigi Hadid took to social media to share an adorable throwback photo to wish her younger sister Bella a happy birthday. Bella turned 20 years old on Sunday (9 October).

The 21-year-old model shared the photo on Instagram, wherein the two sisters can be seen doing stretches while out on a balcony.

Happy Birthday to my baby sister @bellahadid 💥💥 Your beauty and beautiful heart blow me away more every day. You make me more proud than you'll ever know, and I feel so grateful that we get to experience so much by each other's side. 👭 Can't believe you're 20!!!!!!!!!!!!!!!!!!! Love ya miss ya kiss ya 🎈🍾

A photo posted by Gigi Hadid (@gigihadid) on

"Happy Birthday to my baby sister @bellahadid Your beauty and beautiful heart blow me away more every day. You make me more proud than you'll ever know, and I feel so grateful that we get to experience so much by each other's side. Can't believe you're 20!!!!!!!!!!!!!!!!!!! Love ya miss ya kiss ya," Gigi captioned the photo.

Their mother, Yolanda Hadid, also shared an adorable throwback photo of the birthday girl.

"❤️Happy Birthday my sweet Angel..... I pray that each day, love, health and happiness will come your way. Thank you for being YOU, I am so proud of all that you do and all that you are. You are my everything! #ILoveYou #MyBirthdayGirl," the 52-year-old wrote along with the image.

Later, the birthday girl shared a black-and-white photo of her mother cuddling her then-newborn on Instagram. "20 years ago with the woman who birthed me I love you #20," the model shared.

❤️Happy Birthday my sweet Angel..... I pray that each day, love, health and happiness will come your way. Thank you for being YOU, I am so proud of all that you do and all that you are. You are my everything! #ILoveYou #MyBirthdayGirl

A photo posted by YOLANDA (@yolanda.hadid) on

Bella has been dating Canadian singer Abél Makkonen Tesfaye populary known as The Weeknd since May 2015. The model has been coy about her relationship with the Can't Feel My Face hit-maker. But in August, she spoke about her 26-year-old boyfriend in an interview with Glamour magazine.

"I'm dating Abel. I don't see him as The Weeknd. I'm proud of The Weeknd and the music he makes, but I really love Abel," she said. Addressing their red carpet debut at the Grammys in February, Bella said: "It was a big night for him. He has worked so hard, and he did so well that night. As a girlfriend I wanted to be there to support him. Seeing him so happy when he won a Grammy made me so happy."