Benjamin Keough's Girlfriend Says He 'Will Always Be the Love of My Life' in Touching Tribute

Benjamin Keough's girlfriend Diana Pinto has broken her silence following his death.

On Sunday night, a week after Keough — the son of Lisa Marie Presley and grandson of Elvis Presley — died by suicide at the age of 27, Pinto penned a touching tribute to him on Instagram.

"To the most beautiful boy I have ever seen," Pinto wrote in the caption of a photo slideshow. "You make everyone around you light up the second you step into the room. You touch every single soul around you. You love your Sunday morning toons and chocolate milk. I promise to always honor you on Fancy Fridays."

"Your laugh is heard all over the world now," she continued. "You made me the luckiest girl in the world, to have you, to hold you, to love you and to be loved by you are the only things that have ever mattered. You are my whole world and my whole life, you live with me now every day in my heart, in my soul and in my mind."

Pinto went on to call Keough her "travel partner" and "best friend."

"I will cherish all the memories we've made together and keep them close to my heart," she wrote. "I feel your silliness within me still making me laugh. Every second of every day I think of you, now I know the true meaning of grief. Please give me strength to keep going because I don't know how I'm supposed to do this life without you."

Diana Pinto/Instagram Benjamin Keough and girlfriend Diana Pinto

"You will always be the love of my life, my everything," she concluded. "Big pies little pies, te amo mas que el sol y la luna mi amorsito [I love you more than the sun and the moon my love]."

She signed the message, "Love forever, Honu."

In the photo slideshow, Pinto posted several selfies of her and Keough. She also posted a video which shows Keough urging her to join him in the water at the beach, a photo of the message "I Love You Diana" written on what looks like a steamed-up shower door and a solo shot of Keough strumming his guitar on a balcony overlooking the ocean.

Keough and Pinto have dated since at least September 2017, when Pinto posted their first photo on Instagram of them together with friends. According to her LinkedIn page, which has since been deleted, Pinto has worked as a post-production coordinator at Fox.

On Saturday, Keough's older sister, Riley, 31, also spoke out about his death for the first time. In an Instagram post, Riley called him her "twin soul" and "best friend."

"Mornings are the hardest," she wrote. "I forget you're gone. I can't cry because of the fear that I will never stop. A pain that's new to me."

"You. There are no words for you," she continued. "Angel is the closest I could think of. Pure light. Baby brother. Best friend. Wild man. Intellectual. Witness to my life. Twin soul. Protector. Too sensitive for this harsh world. I hope you give me strength to endure the giant hole you've left in my heart. I hope you give me the strength to eat. I hope you're cradled in love. I hope you feel my love. I hope you feel god. You are god. I can't believe you've left me. Not you sweet Ben Ben. Anyone but you. I guess this is true heartbreak. I hope we meet again."

RELATED: Riley Keough Shares Touching Tribute to Late Brother Benjamin: 'This Is True Heartbreak'

Lisa Marie, 52, shares Keough and Riley with ex-husband Danny Keough. She also has 11-year-old twins Harper and Finley, whom she shares with ex-husband Michael Lockwood.

Following Keough's death, Lisa Marie's rep, Roger Widynowski, told PEOPLE that the star is "beyond devastated."

"She is completely heartbroken, inconsolable and beyond devastated but trying to stay strong for her 11-year-old twins and her oldest daughter Riley," Widynowski said. "She adored that boy. He was the love of her life."

Lisa Marie Presley / Instagram Lisa Marie Presley (left) and Benjamin Keough

Benjamin's friend, musician Brandon Howard, recently told PEOPLE that the pressure to live up to the Presley family name "absolutely" contributed to Benjamin's struggles.

"That kind of pressure is definitely a part of what happened," he said. "It's a tough thing when you have a lot of pressure with your family and living up to a name and an image. It's a lot of pressure. It's almost like you're pressured into having to be a musician, having to be an actor. It was good for him to go around the world and discover himself and have his own friends. You never know what triggers it. You never know ... It's so random."