Charmian Carr, who played Liesl, the eldest of the Von Trapp children in The Sound of Music, has tragically passed away at the age of 73.
She died after complications from a rare form of dementia, her representatives have said.
On her official website, a statement from the site’s manager Steve Hughes reads: "Me and my family are so sad to have to post this message and will miss her dearly.
“We had the gracious opportunity to stay at Charmian Carr’s house several times while we worked on different projects for her. And we travelled to New York with her on another occasion.
“She was such a nice, cheerful person. We always loved The Sound Of Music and still do."
Kym Karath, who played Carr’s on-screen sister, Gretl, in the movie, took to Twitter to express her grief over the loss of her life-long friend.
She wrote: “It is with infinite sadness that I share the tragic news that the precious & exquisite Charmian Carr , beautiful Liesl , has passed away.”
It is with infinite sadness that I share the tragic news that the precious & exquisite Charmian Carr , beautiful Liesl , has passed away .— Kym Karath (@KymKarath) September 18, 2016
Sharing a photograph of herself with Carr, Karath added: "She has been like a sister throughout my life."
Meanwhile Ted Chapin at Rodgers & Hammerstein paid tribute to Carr on the official website, saying: "It's always sad when a member of the family passes away - and in the case of the 'family' of the movie The Sound of Music, it's especially sad when it is the first of the group to go.
“Charmian Carr played the oldest Von Trapp child, and in some ways she maintained that role in real life - guiding, cheering, supporting and generally being there for the rest of her 'sisters' and 'brothers.'
“She was a great ambassador, and we had so many good times together, either working on Sound of Music related events, or, something I will always remember, arranging for her to be a special guest at New York's Symphony Space's Wall to Wall Stephen Sondheim, reminding that audience that Charmy did, in fact, star opposite Anthony Perkins in the 1967 TV musical Evening Primrose.
“I will miss her charm and her spirit. We all send condolences to her family."
Carr was just 21 when she took on the role of Liesl von Trapp in the Oscar-winning musical, after her mother convinced her to audition – despite the fact that she had undergone no acting or singing training.
She was quickly awarded the role, and soon found herself starring alongside Julie Andrews and Christopher Plummer.
Her most notable moment in the 1965 film came in the iconic gazebo scene opposite actor Daniel Truhitte, during which she sang the beautiful song, I Am Sixteen Going on Seventeen.
The actress later wrote two books about her experience - Forever Liesl and Letters to Liesl - and frequently appeared at events commemorating the movie.
Speaking in 2005 at a sing-along performance of the film at the Hollywood Bowl, she said: "I tell people that they should consider sing-a-long Sound Of Music like going to a therapist.
"It's just a kind of therapy. They can move around. They can dance and talk back to the screen. They can skip their appointment with the shrink that week."
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Her only other major role was in the Stephen Sondheim television musical Evening Primrose, before she launched her own successful interior design firm in Encino, California.
Among her various celebrity clients was Ernest Lehman, who wrote the screenplay for the Sound of Music, and Michael Jackson.
She is survived by two children and four grandchildren.