She declared sister Gigi her 'best friend' and confidant as she spoke about their shared experiences in London last week.
So there was no question that jetset sweetheart Bella Hadid would be back in the States for her older sibling's 22nd birthday at the weekend.
Having spent the week in Europe - from Paris to London and back again - to promote her new Dior beauty collaboration, Bella flew back into New York City and was seen out celebrating with mum Yolanda and sister Gigi in Midtown by Sunday afternoon.
Naturally, the young model looked incredibly chic and stepped out wearing a denim boilersuit with red floral embroidery.
A tricky look to pull off, the stunner highlighted her model proportions with a belt at the middle.
She carried a Chanel quilted overnight bag; a coveted designer accessory that dramatically offset her masculine biker boots.
It was a different story for birthday girl Gigi, who was firmly embracing her girlier side in bright pink.
From top to toe she wore fuchsia, matching a light pink Alice + Olivia duster coat with fur-lined Gucci loafers in the same shade.
Gigi was ringing in her 22nd in the company of family, friends and of course, boyfriend Zayn Malik, who posted a touching dedication on Instagram.
'happy birthday to my everything ' he wrote, posting a black and white picture of him planting a kiss on her cheek.
Former One Direction star Zayn wasn't the only one with gushing words about the queen of the catwalk.
Just last week, as she promoted her new beauty link-up with Dior Show's Pump n Volume mascara, Bella told MailOnline: 'Gigi is my best friend and I love her to death.
'She's been through everything I'm going through now because she's been in the business longer.
'If I'm sad I'll call her and she always makes me happy again. She's the best, I love her.'
Bella similarly didn't spare any kind words in her touching Instagram tribute, in which she shared precious pictures from the family album.
'Happy birthday to my best friend FOR F**king LIFE!!!!!!!! ' she wrote. 'My role model! My person. I feel so lucky every day to call you my sister.
'I didn't know anyone could be so generous, smart, funny, talented, hard working, artistic, loving, respectful AND beautiful all at the same damn time!!!
'You make me laugh until I pee and even when I don't want to smile, you are just about the only person that can make me.
'Every one that knows you, immediately feels the incredible energy that radiates throughout you.
'Thank you for always being yourself, nothing more and nothing less. You are my other half & I don't know what I would ever do without you. I love you with all of my heart Squeegee.'
By Becky Freeth
© Associated Newspapers Ltd.