"Thank you for being born so that I could be born that was very sweet of u," Bella wrote on Instagram April 23. "Thank you for being the best sister, mom, daughter, human bean ever. You teach me something new everyday and sometimes I just smile because I feel so lucky to be your baby sister."
She added, "I'm sitting next to you right now so don't make it weird when you read this. I love you."
Along with the heartwarming message, Bella, 25, included a carousel of photos of the tight-knit sisters, including several snaps from when they were kids and others at various modeling jobs as adults.
Alana reposted the same photo on her own Instagram, calling her little sister her "sweet little angel."
"I already sang you a horrible rendition of happy birthday and told you my wish from my heart," the 36-year-old wrote. "I feel extra nostalgic this year maybe because it's the first year in a long time I haven't been with you on your birthday. It's so amazing to watch you grow up, to see you flourish, to be there with you and for you. I am just so proud of you and you will always be that tiny squishy sweet baby I loved to hold, and you are at the same time the most amazing woman who has accomplished so much that I truly admire.
She added, "I adore you my Jelena. Never ever ever change."
This morning of Gigi's birthday on April 23, Bella was spotted out at the Balloon Saloon in New York City where she picked up a bunch of balloons, including one shaped like a hot dog, before taking them to her sister's apartment.
Earlier this week, Gigi joked about wanting close pal Blake Lively to sling drinks at her birthday party after the actress posted a new commercial for her non-alcoholic mixer brand, Betty Buzz, on Instagram. In the clip, Blake pours one of her fizzy drinks and comments on its bubbly nature as a bubble machine whirrs behind her.
"Hi what's ur rate for 3 hrs of bartending 4 bday weekend," Gigi commented. "Nothing hits like one mixed by B."
"I've been reminded that when we get time with people,"she shared in February, "just really appreciate it and take it all in and try not to wish away moments. Even if there's something hard, find something beautiful in it."