Judy Parfitt has teased 'Call the Midwife' fans that "anything can happen" to her character in the 12th series.
The 87-year-old actress has previously admitted she is surprised her character Sister Monica Joan hasn't been killed off, and now the star has admitted her alter-ego starts to "lose the plot" at times in the upcoming season.
She said: "Oh anything can happen to Sister Monica.
"She goes through various things, it is really difficult to explain because she has come and gone health-wise.
"I think I have said before when she is tired, or stressed, or upset or ill that she begins to lose the plot, but I do have quite a few varied things to do in this series."
Judy also teased one "lovely" episode in which Sister Monica Joan befriends a dog, and the actress found it "extraordinary" just how well the pooch could act.
She added to Express.co.uk: "It is lovely and very fulfilling and I have a lovely episode with a dog, lovely dog. I know I am on to a winner there.
"He was adorable, I love dogs but it is just extraordinary how that dog was taught.
"You didn't worry that this dog was being naughty, she would say, 'Go back to your mark paddy' and he would go and stay there."
In December last year, Judy said she was "surprised" that Sister Monica - who she has portrayed in the BBC show since 2012 - was yet to meet her maker.
She said: "I think about hanging up my wimple because it's uncomfortable to wear, but not retiring.
"I'm surprised they haven't killed Sister Monica Joan off. But as long as I can walk a straight line and remember my words, I'll be there."
When asked why her character is so popular with the show's followers, she said: "I think it's her innate innocence, her kindness and her struggles - and because she's eccentric and obviously educated, she uses words nobody else uses any more. And, of course, she has a love of cakes and biscuits.
"It got to the point where every time I went to the supermarket, staff would say: 'The cakes are over there.' "