Melissa Gilbert is remembering Anna "Patty Duke" Pearce after her death on Tuesday morning.
The Little House on the Prairie star tells ET in a moving statement, "Anna was my dear friend, teacher, and a second mother."
"Her passing leaves a huge hole in my heart. She helped raise me to be the woman I am today," the 51-year-old actress continues. "She was so loved by so many people including me."
WATCH: Anna 'Patty Duke' Pearce, Oscar-Winning Actress, Dies at 69
Gilbert, who shared the screen with Duke in 1979's The Miracle Worker, goes on to reflect on Duke's achievements as an actor, her family, and her mental health advocacy work. Read on for her entire statement.
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"She had a mind-boggling depth of talent, a fantastic sense of humor and survived being a child actor in the worst of circumstances. Anna won every award possible as a performer and as a humanitarian, and it was all well-deserved -- she was an extraordinary human being.
She got so many people to see mental illness as what it really is, and led the effort to de-stigmatize it. She truly understood mental illness at its core and worked her entire life to help those who suffer from it.
She inspired me to be a better actor, a better mother, and a better person. She was an advocate and activist, and my mentor. I was just so lucky to have known her for almost 40 years. She loved people ferociously and adored her family. I was blessed be a part of that.
Today, my heart aches for her big beautiful family, but I know she’s in a better place. I will miss her every day but I will find comfort in the words of Helen Keller: "The best and most beautiful things in the world cannot be seen or even touched-they must be felt with the heart.'"
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A rep for Duke tells ET she died from sepsis due to a ruptured intestine.
Her family told ET in a statement, "This morning, our beloved wife, mother, matriarch, and the exquisite artist, humanitarian, and champion of mental health, Anna 'Patty Duke' Pearce, closed her eyes, quieted her pain and ascended to a beautiful place," adding, "We celebrate the infinite love and compassion she shared through her work and throughout her life."
In the wake of Duke's death, Hollywood has been paying their respects. Actor William Shatner tweeted, "Very saddened on the passing of Patty Duke. She was a wonderful friend on Twitter. Condolences to her family."
Marlee Matlin also shared her love on Twitter, writing, "Brave, outspoken & humanitarian who played Helen Keller in "Miracle Worker," Oscar winner Patty Duke passed. I will miss her. RIP."
After Duke's son, Sean Astin, posted a moving remembrance to Facebook, his Lord of the Rings co-star, Elijah Wood, reached out with support, tweeting, "My heart goes out to @SeanAstin and the entire family. #PattyDuke."
Glee star Chris Colfer wrote, "So sad to hear of Patty Duke's passing. She was a wonderful and talented person. I loved getting to work with her. XO."
"Rest with the Angels, Patty Duke. Thoughts and prayers are with all that love her," Alyssa Milano wrote on her Twitter.
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The Academy tweeted, "Thank you Patty Duke for all that you've given us. You'll be missed."
See more stars remembering Duke below.
Watch the video below for more on the Hollywood icon's death.