The British actress passed away of natural causes at an assisted living home in L.A., her manager Mitch Clem confirmed to us Thursday ... adding she'll be buried next to her father in the UK.

Mitch paid tribute to Glynis in an emotional statement: "Glynis powered her way through life with intelligence, wit, and a love for performance, affecting millions of lives. She entered my life early in my career and set a very high bar on how to navigate this industry with grace, class, and truth. Your own truth. Her light shined very brightly for 100 years.

He added, "She had a wit that could stop you in your tracks powered by a heart that loved deeply and purely. Today is a somber day for Hollywood. Not only do we mourn the passing of our dear Glynis, but we mourn the end of the golden age of Hollywood."

Glynis was born in South Africa, but her family settled in England, where she worked as an actress for 20 years before scoring a starring role in Disney's adaptation of P.L. Travers' "Mary Poppins" novels.

During the rest of her 8-decade career on screen and stage, she earned a Tony for her role as Desiree Armfeldt in the original Broadway production of Stephen Sondheim's "A Little Night Music" ... where she sang "Send in the Clowns." Sondheim wrote the song especially for Glynis to perform.

Her role in the 1960 film "The Sundowners" earned her an Oscar nom ... and was just one of more than 60 films she starred in, along with "While You Were Sleeping."

Glynis' TV credits include "Murder, She Wrote," "Cheers" and "The Love Boat." Her final onscreen appearance came in 1999's "Superstar" ... where she played Grandma.

Glynis celebrated her 100th birthday in October ... quipping that she didn't feel any different after turning the milestone age -- adding that she looked good for every age.