Kaia Gerber reveals the depth of her grief over loss of older brother Presley in emotional tribute: 'I am, quite literally, down on my f***ing knees.'

Kaia Gerber has publicly paid tribute to her older brother Presley for the first time since his death on September 20.

The model, 25, shared home video footage of herself and Presley as children along with a handwritten letter in which she revealed the depths of her grief at his passing.

'prez, i don't have the words,' she began. 'how naive of me to believe that language could transcend grief.

'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.'

It came shortly after her famous mother Cindy Crawford posted a statement to Instagram on behalf of herself and husband Rande Gerber, expressing their devastation at the loss of their only son.

Presley died of a suspected overdose after going into cardiac arrest while staying at the Santa Monica rehab facility Resolutions Li. He was 27.

He had been open in recent years about his struggles with his mental health and drug addiction. 

Kaia poured out her heart in the four-page letter as she reflected on never having known a world in which Presley didn't exist. 

'you know how much i loved being your sister. it has always been, and will forever be, my favorite thing about myself,' Kaia wrote. 

'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.'

The heart-wrenching note went on: '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***ing wish you hadn't gone first this time,' Kaia wrote.

Kaia shared that loving her brother 'was the easiest thing in the world.'

'i was born loving you. i will die loving you. there was never anything else.'

She concluded:  'my best buddy, my great protector, the hardest i've ever laughed and the one true love of my life - you lit all of my candles and took all of my monsters away.

'and i love you. and i love you. and i love you. only you know how much. thank you for being here.'

Earlier on Sunday, Crawford and Gerber issued a joint statement shared on Instagram in which they said that they are 'beyond heartbroken' at the loss of their only son.

'We feel so blessed to have had Presley in our lives for 27 years. He is a sweet, beautiful soul who loved and is loved, now and forever. We are so proud of how he showed up in the world, with kindness and vulnerability.'

The statement continued: 'We are grateful for the outpouring of love and support from so many who know and love our family and even strangers who feel our pain. Til we meet again our sweet boy. We love you forever, Mom, Dad and Kaia.'

In footage obtained by TMZ from the night before he died, Presley was seen giving a solo tour of the sober home he had been dropped off at.

Taken around 10pm, he appeared to be under the influence as he stared into the camera with noticeably glazed eyes. Throughout the video, he panned the camera around a bedroom and multiple areas of the residence.

Presley reportedly 'got high' on Saturday afternoon and became concerned he was losing control, insiders claimed to TMZ. His sober coach had called the living facility and asked if he could bring Presley in – though he made it clear that Presley was high on drugs – and the facility's admissions officer reportedly agreed, the outlet reported.

The sober coach had reportedly planned to take Presley to a rehab facility the following Monday but needed a temporary hold for the weekend and subsequently left him at Resolutions Living, according to insiders. Sources claimed that Presley continued using drugs inside the sober home.

A final confirmation of any substances that may have played a role in his death will be revealed upon the release of the Medical Examiner's toxicology report. 

His remains were 'cremated' just days after his passing at the Rose Family Funeral Home, per a death certificate obtained by TMZ. Crawford and Gerber will reportedly keep their son's ashes at their residence.

The Daily Mail previously obtained audio of the 911 emergency dispatch call made from the Santa Monica rehab, in which an automated voice could be heard saying 'cardiac arrest' followed by 'overdose.'

The first call was made on Sunday, September 20 at 9.35am regarding a cardiac arrest, however, just three minutes later it was upgraded to an 'overdose,' then finally at 9.40am the priority was upped once again as it was 'upgraded.'

Presley, who started modeling from a young age like his sister, had been open about his decade-long struggle with drug addiction and mental health problems before his death. 

Last November, Presley revealed he had taken a step back from social media to 'take care of my own mental health for a bit.'

One month later, he opened up about his personal life in a candid social media video and started sharing 'Mental Health Mondays' videos on his Instagram. In one, he listed the medication he takes for 'night terrors' and 'panic attacks,' saying his use of medication had been 'fluctuating up and down depending on what's been going on in my life.'

Earlier this year, he posted about having a 'Pre-ibogaine flood dose' at a Mexican treatment clinic, a single, high-dose administration of the naturally occurring psychoactive substance ibogaine that is reported to help with withdrawal symptoms. The high dose is designed to induce a profound 'reset.'

Presley's parents and his sister Kaia praised him for his 'courage' in response to his post about starting the treatment in March.

Crawford commented: 'You are a warrior! Walked thru the fire to find yourself! So proud!' while Kaia added: 'That's my brother I am so damn proud.'

And Kaia wrote: 'I'm so proud of you and your courage. Facing what's hard takes real strength and watching you find your way back to yourself is everything. I love you so much.'

Presley's death came just weeks after Kaia opened up about the enormous toll her brother's struggles had taken on their famous family.

'When something like that happens in a family, it kind of levels everyone,' Kaia told Vogue.

But for all the concerns for Kaia, our source said: 'Kaia has not had it easy in her 25 years, but she will hang in there, she is a very strong person.'

The Daily Mail has reached out to representatives for Kaia and Crawford for comment.

If you or someone you know is struggling with mental health issues, emotional distress, alcohol or drug use concerns, you can also visit 988lifeline.org. You can also call, text or chat with a counselor by texting 988.