Bryony played the quiet and sensitive character for five years, from 2012 to 2017.
But will she ever return? And who does she play in Death in Paradise?
Here’s everything you need to know!
Who is Bryony Hannah?
Bryony was nominated for an Olivier Award for her theatre work.
She played Sister Mary Cynthia in BBC One’s Call the Midwife, probably the role she is most famous for.
The RADA-trained actress has appeared on TV, stage and film.
What else has she been in?
Viewers know Bryony for her role as Sister Cynthia Miller in Call the Midwife.
However, she has also starred in Jupiter Ascending, Cemetery Junction and Unforgotten.
Those with kids might recognise her as the voice of Padget in Bing on CBeebies.
How old is she?
Bryony was born in 1984, and is 37 years old.
She was born in Portsmouth, Hampshire, the daughter of a teacher and a retired Royal Navy lieutenant-commander.
Is she married?
Bryony is extremely private about her personal life, and has not revealed her marital status.
However, we do know that she gave birth to her first child in 2014.
What happened to Sister Mary Cynthia in Call the Midwife?
Bryony’s character was introduced as Nurse Cynthia Miller in 2012.
However, during the course of the show, Cynthia decided she was being called to a religious life, and became a nun.
Her character lived as a nun at Nonnatus house, where she also worked as nurse.
In June 2017, after five years on the BBC One show, Bryony announced she was leaving Call The Midwife.
She left at the end of series six and did not appear in series seven.
Bryony exited the show to concentrate on other work, and went on to focus on her theatre career.
Her character went though all sorts of trauma.
She was targeted by a serial attacker and knocked unconscious.
She returned to her colleagues with a battered appearance and bite marks on her neck.
Sister Mary Cynthia eventually reported the matter to police, and helped them find the criminal.
In series six, Sister Mary Cynthia convalesced at the Linchmere Hospital, an austere mental institution.
She received electro-convulsive therapy (ECT) for her depression.
Who does Bryony play in Death in Paradise?
An archaeologist is found poisoned during a dig, and Bryony Hannah’s Rebecca Morley is one of the suspects – as is Luke Pasqualino’s Ed Lancer.
However, despite an early confession, the team realise they have little to no evidence.
Death in Paradise airs on Thursdays at 9pm on BBC One.
What do you think? Leave us a comment on our Facebook page @EntertainmentDailyFix.