Actress Margaret Tyzack has died after a short illness, her agent said.
The 79-year-old, who made her name in the Forsyte Saga, recently appeared in EastEnders playing Lydia Simmonds, but had to withdraw after a short stint.
A statement released by her agent said: "Margaret Tyzack CBE, the much-loved and respected actress, died peacefully at home on Saturday June 25 with her family by her side.
"Maggie will be greatly missed by her family and friends and will be remembered for her outstanding contribution to the world of theatre, film and television and for the support and inspiration she gave to young actors."
It is believed she had been suffering with cancer.
She was awarded the CBE last year.
Her career took off more than 40 years ago when she landed the role of Winifred, Soames's sister, in The Forsyte Saga in 1967.
The TV serial was so popular vicars complained it was affecting attendance at Sunday evening services.
Bryan Kirkwood, executive producer of EastEnders, said: "I'm so sad to hear the tragic news about Margaret.
"Even though we only worked together for a brief time, Margaret made a great impact with EastEnders. She was a fabulous actress and an inspiration to us all and she will be sorely missed."