Elvis Presley's Ex Linda Thompson 'Devastated and Shocked' by Death of Lisa Marie

Lisa Marie Presley is being remembered by those who knew her best.

Linda Thompson, who dated Lisa Marie's father Elvis Presley from 1972 to 1976, tells PEOPLE that she is "absolutely devastated and shocked" at her death on Thursday aged 54.

"I was so happy to see her at Graceland to celebrate what would have been Elvis's 88th birthday, and then, of course, at the Golden Globes," Thompson, 72, adds about Lisa Marie, who she first met as a young girl.

"She seemed to be on a more positive trajectory emotionally after the unfathomable loss of her beloved son, Benjamin," continues Thompson in reference to the tragic July 2020 suicide of Lisa Marie's late son Benjamin Keough.

"Lisa and I kept in touch off &  on for all these years — most recently by text. In fact, the very last text to me was a simple 'Love you Linda' with a heart emoji."

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Brandon Williams/Getty; Kevin Winter/Getty

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"Lisa Marie was so much like her daddy it was uncanny," adds Thompson, who first met Elvis in 1972 shortly after he separated from Priscilla Presley. "She had his deep, soulful eyes, his pouty lip, and his raucous, irreverent sense of humor. She was a beautiful contradiction like Elvis… complicated in her simplicity. She was brutally honest, straightforward, loving and loyal. I don't think there was a phony cell in her body. I believe she lived her life authentically."

Tom Wargacki/WireImage

Following her relationship with Elvis, Thompson went on marry Caitlyn Jenner in 1981 before she transitioned. The pair had two kids together, Brandon and Brody, before separating in 1986, and before Thompson married David Foster from 1991 to 2005.

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The songwriter and actress remained in touch with Lisa Marie throughout and paid her respects on Instagram Thursday, sharing an image of Elvis holding his young daughter with the caption "My heart is too heavy for words…💔😥."

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Frank Carroll/Sygma via Getty Lisa Marie and Elvis Presley

"I will always be profoundly grateful to the little nine-year-old Lisa Marie, who had the presence of mind to call me from Graceland the fateful day her daddy died to give me the news," Thompson tells PEOPLE. "I was the first person she called. To me, that spoke volumes of how close we were, and how sure she was of my love for her daddy. In fact, if there is any solace to be found now, it's in my knowing that Lisa Marie was sure I loved her and her daddy, without reservation and without any agenda…"

"When Lisa was a little girl, I played Santa Claus to her four times at Christmas, and I was the Easter bunny on Easter, hiding eggs around Graceland," continues Thompson. "We took golf cart rides together, and Elvis trusted me and my love for her enough that he let me drive her to the movies, and to visit my family."

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"We took bubble baths together, tearing rose petals off bouquets that fans had sent to Elvis and scattering them in the big tub. She shared her little girl secrets with me, and after she was grown, she wanted to introduce me to her loves."

"She, Michael Jackson and my family all spent time together in New York. She brought Nicolas Cage to my house for me to meet him and get my opinion. She came to several of my parties, and on one occasion, her daughter Riley insisted upon sleeping over at my house. She was about nine years old then herself, so Lisa Marie let her have a sleepover. Those are all precious memories for me."

"Lisa Marie was, without a doubt, the greatest love of Elvis's life," continues Thompson. "I think most parents understand that unconditional love that can compare to no other. He was happiest and felt most complete when she was with us. The three of us would press our foreheads together, rocking back-and-forth… We called that mugging. I could hear Elvis grind his teeth, the love was so intense."