Vanessa Redgrave is to appear in Call The Midwife.
The 77-year-old actress, who narrates the series as a mature Jennifer Worth, will make her first appearance on the show in this year's Christmas special.
Filming on the fourth series has just begun and will see the introduction of two new characters, Nurse Phyllis Crane, played by 'Lark Rise to Candleford' star Linda Bassett and Nurse Barbara Gilbert, played by 'Fresh Meat' actress Charlotte Ritchie.
Producer Pippa Harris said: "We're all delighted to be welcoming Vanessa Redgrave on screen, having hugely enjoyed her narration of the series to date.
"It's also terrific that [show creator and executive producer] Heidi Thomas has created two wonderful new characters for the series, and that we're fortunate enough to have Linda Bassett and Charlotte Ritchie joining our regular and much-loved team at Nonnatus House."
Heidi added: "The medical, social and emotional stories at the heart of 'Call the Midwife' continue to inspire and compel me. The Nonnatus House nurses and midwives feel like my best-loved friends."
Vanessa has voiced an older Jennifer Worth on the show since its inception, while Jessica Raine played a younger version of the character before quitting at the end of the third series earlier this year.
The new series will take place in 1960 and depict big changes to London's East End, where the show is set.
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