Bella and Gigi Hadid. Picture: Bang Showbiz

American model Bella Hadid has revealed on Instagram that she is "beyond proud" of her sister Gigi.

The 21-year-old model and Gigi, 22, have both recently been appearing at Milan Fashion Week in Italy, and Bella has taken to her Instagram account to post a celebratory video of them opening a bottle of Champagne backstage at a show and to lavish praise on her sibling.

READ: Gigi Hadid releases another special collection with Vogue eye-wear

Alongside the video, the brunette beauty wrote: "Post- sappy speech before the show..And I've been telling you all night... but @gigihadid I am so beyond proud of the hardworking, kind, talented, smart, funny woman that you are ETCETCETC... (your perfect face being the least of your attributes) congratulations on your 4th and final tommyxgigi collection....You exceeded all expectations, not only from me but everyone around you. I am not surprised that you had a another perfect show but yet again, you have surprised me, as you do every day [love heart emoji] (sic)"

Bella subsequently revealed that she was writing her post while they were both on a plane returning home.

She continued: "I love you to the moon and back tiny cub.

Also you're sitting next to me sleeping on the plane like the cutest bear ever and I'm just thinking how lucky I am to have u as a sister !. Love you. @tommyhilfiger (sic)"

Earlier this month, Yolanda Hadid revealed she taught her daughter Gigi how to become a successful model.

The 54-year-old star - who is a former model herself - said Gigi has been "groomed" to become a runway icon since she was a child.

Yolanda shared: "Gigi always wanted to be a model so I groomed her in a playful way, dressed them up and did little campaigns with them. But I always said, that you can't model until you're 18. 

"Gigi would fight with me over it and tell me that there were loads of 16-year-olds modelling and I would tell her, 'well that's too bad.' I've been there and I know what goes on. Now she's older, she thanks me for giving her the opportunity to be a kid - to run around the farm make-up-free for longer."