The 25-year-old model paid a heartfelt tribute to her sibling after he died at the age of 27 on September 20.
She remembered him as her "ultimate teacher" and the "love of [her] life" as she expressed her regret that he had died first, after she had spent so many years following in his footsteps.
Alongside a throwback photo and a video of them dancing as children, she shared a series of slides on Instagram.
"Prez, I don't have the words, and maybe the tiny mercy is that we didn't need them all along. Words fail and words subtract and words summarize and words always lack truth. And how naive of me to believe that language could transcend grief," she wrote.
"I've read all of the books and I have none of the answers. My articulation is no match against this, the magnitude of losing you. I am, quite literally, down on my f***ing knees.
"You know how much I loved being your sister. It has always been, and will forever be, my favorite thing about myself.
"I came into this world with a white-knuckle grip around you. I had more love for you than I knew what to do with. and now that it has nowhere obvious to go, I'm certain it's going to swallow me whole.
"You were my ultimate teacher while you were here and now I'm left wondering what I could possibly be taught in your absence, and I keep thinking about how when we were little, I got scared before getting my ears pierced, so you went first. You always went first.
"But when I held the earring they took from your body, all I could think was: that belongs to you. And I really f***in g wish you hadn't gone first this time.
"To say loving you was the easiest thing in the world would imply that it required any effort at all. I was born loving you. I will die loving you.
"How to be your sister in a world that I can't reach for you in. I don't know how to do that yet."
The model and actress insisted she would "choose" to go through her grief again if it was the price she paid for their many years together.
"My darling brother, I do adore you. I love my brother. My brother is dead. And this party sucks so bad without you, Prez."
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