On Wednesday, October 21, Presley, 52, posted a picture of Keough from a previous birthday, along with a touching caption to Instagram. "My beautiful beautiful angel," she began.
"I worshipped the ground you walked on, on this earth and now in Heaven. My heart and soul went with you," she added. "The depth of the pain is suffocating and bottomless without you every moment of every day."
The singer and daughter of Elvis Presley, added that she "will never be the same."
"Please wait for me my love, and hold my hand while I stay to continue to protect and raise your little sisters and to be here for Riley. I know you would want that," she said. "Happy Birthday my sweet sweet Boy. You were much too good for this world."
Fans offered their condolences to the grieving mother on social media.
"We’re with you Lisa and thinking of your Benjamin today. Hope you feel our love!" one wrote.
"Sending you so much love I am so sorry for your loss. RIP Angel," another fan wrote.
Presley's representative, Roger Widynowski, told PEOPLE earlier in the year that she was crushed by the death of her son.
"She is completely heartbroken, inconsolable and beyond devastated but trying to stay strong for her 11-year-old twins and her oldest daughter Riley," the rep said. "She adored that boy. He was the love of her life."
The mother and son were extremely close and even got matching Celtic knot tattoos on Mother's Day 2009 that represented "eternal love and connection."
Grandmother Priscilla Presley previously wrote after his death that she was "trying to put all the pieces together of all the possible ways he has penetrated my soul. Each day I wake up I pray it will get better."
Sister Riley Keough took the time to post her own tribute to her brother. "Happy Birthday beautiful angel," she captioned a short collection of images on Instagram. She also shared sweet throwback pictures of her brother on her Instagram Story. She added s heart emoji and two storm emojis — a nod to his middle name, Storm.
His ex-girlfriend Diana Pinto also shared a tribute, some of which was re-shared by Keough on her Instagram Story. "Happy birthday my love. Not much to say just a really hard day. And isn’t it ironic World Series Tampa Bay v Dodgers this year, I bet you’re getting a kick outta that. I love you," she captioned a slew of photos.
Benjamin was Lisa Marie's second child with Michael Lockwood. The former couple share four children together, Riley, 31, Benjamin and 11-year-old-twins Harper and Finley.
Our thoughts are with Presley and her family.