Lisa Marie Presley's Half-Brother Navarone Garibaldi Says He's 'Lost for Words' After Her Death

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Navarone Garibaldi is mourning the loss of his half-sister, Lisa Marie Presley.

The son of Priscilla Presley paid tribute to Lisa Marie after she died on Thursday at age 54, sharing a throwback photo of the late singer-songwriter and himself when he was a child.

Calling her "Big sister," Garibaldi, 35, wrote in the Friday Instagram caption, "I hope you are now at peace and happy with your Dad and your son by your side." (Lisa Marie's son Benjamin Keough died by suicide at age 27 on July 12, 2020, and her dad Elvis Presley died in August 1977 when Lisa Marie was 9 years old.)

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"I know the past couple of years weren't easy for you, and I wish things had been different between us," he continued. "Regardless, you are my sister, and I'm sending love and prayers for your journey home. I still can't believe this, I'm lost for words. Love you sis. Beijos. 💔."

Priscilla, 77, shares Navarone with her ex-Marco Garibaldi.

Lisa Marie died on Thursday after being rushed to the hospital for a possible cardiac arrest. Priscilla confirmed her daughter's death to PEOPLE in a statement.

"It is with a heavy heart that I must share the devastating news that my beautiful daughter Lisa Marie has left us," began Priscilla.

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"She was the most passionate strong and loving woman I have ever known. We ask for privacy as we try to deal with this profound loss. Thank you for the love and prayers. At this time, there will be no further comment."

Lisa Marie made her final public appearance at the 80th Golden Globe Awards earlier this week. She attended the show with her mother to cheer on Austin Butler, who won best actor in a drama that evening for his portrayal of Elvis in the Baz Luhrmann film.

When congratulated by PEOPLE on Butler's win and asked how she was feeling, Lisa Marie smiled and said, "I'm so happy."

RELATED VIDEO: Lisa Marie Presley Said Father Elvis Would 'Be Proud' of Film Starring Austin Butler

At a party celebrating the Elvis film the weekend before the Golden Globes (Jan. 8, Elvis' birthday), Lisa Marie addressed the attendees and said her dad would be proud of the movie.

"I'm so overwhelmed by this film and the effect that it's had and what Baz has done, Austin's done," she said at the gathering. "I'm so proud, and I know that my father would also be very proud. ... I'm overwhelmed with gratitude, so thank you."