Ferguson, 63, spoke at Presley's Graceland memorial service on Sunday in an effort to "celebrate the extraordinary Lisa Marie" at an event full of her closest loved ones.
"I stand here with great honor because we called each other 'sissy,' and I've been with you all for all your lives really," the Duchess of York said.
Sarah Ferguson Instagram Sarah Ferguson and Lisa Marie Presley
"Sissy this is for you with affection," Ferguson continued. "My late mother-in-law used to say that nothing [that] can be said can begin to take away the anguish and the pain of these moments, because grief is the price we pay for love. And how right she was."
The public service was held on the front lawn at the Graceland mansion in Memphis, Tennessee, as family members Priscilla, daughter Riley Keough, half-brother Navarone Garcia, ex-husband Michael Lockwood, their 14-year-old twin daughters Finley and Harper and late son Benjamin's girlfriend Diana Jay, all came in support of Lisa Marie. Elvis' only daughter died Jan. 12 after being rushed to a Los Angeles hospital for a possible cardiac arrest at 54 years old.
"We look at Priscilla as a mother to Lisa Marie, we look at Lisa Marie and say, 'You lost a son,'" Ferguson said of Presley's son Benjamin who died in 2020. "Mothers losing children — there are no words for it. So today we talk about action. Action is the way we can go forward, we can light the flame. So for Riley, for Harper and Finley and the entire family, we march forward in support of you. All of us are with you. If you just put out your hand we will be there. I will definitely be there."
Jason Kempin/Getty Sarah Ferguson
Ferguson went on to read a poem by George Frost, the son of British TV journalist David Frost, which he wrote for his late father. "I've had my life and enjoyed every second. But as it is, another life beckoned," she read. "It's important to know that I have not gone. And I hope that, on you all, my light has shone. Stay in the sunshine, rest never in the shade. Don't curse my absence, as this light you'll evade. I live in the smiles, the moon, stars and sky. And I feel eternal pride as I watch you all fly. And for my darling children who wonder what to do. Just have a wonderful time, as I will, living through you."
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The Duchess of York previously toasted Presley with one of the many tributes remembering her late friend last week. In it, Fergie called her "sissy" and promised she'd "continue to say hello to you every day."
"You were my sissy, an amazing mother to Ben, Riley, Harper and Finley and a superbly loving daughter to Priscilla," Ferguson wrote. "You have been my devoted friend for many years and I am here for your family to support and love them."
She added, "I am deeply saddened my sissy, you are in my heart."
Per the Daily Mail, Fergie and Presley are believed to have met in 2009, and Presley attended her 50th birthday party in London the same year.
The daughter of Elvis died earlier this month just days after Austin Butler took home a Golden Globe on Jan. 10 for playing her father in Baz Luhrmann's film named after him. Butler gave a special shout-out to Presley's family on stage at the event. After her death, Butler said that his "heart is completely shattered."
"I am eternally grateful for the time I was lucky enough to be near her bright light and will forever cherish the quiet moments we shared," the actor said in a statement shared with PEOPLE.