Keeley Hawes has promised the final series of "The Durrells" will be "dark".
The ITV drama series will skip ahead from 1937 to 1939 for the fourth season and the episodes will see the family's tranquil life on Corfu disrupted when World War II breaks out.
Keeley - who plays Louisa Durrell - said: "It gets a little bit dark for the Durrells, which has always been a light and lovely show.
"The war is approaching, and they have to deal with that - as indeed the Durrells themselves did."
In real life, the family arrived on the Greek island in 1935 and stayed until the war began, which prompted most of them to return to safety in England, though Larry stayed behind and later escaped to Egypt and Margo headed to South Africa.
Keeley and her co-stars - including Milo Parker, Josh O'Connor, Daisy Waterstone and Callum Woodhouse - feel "lucky" to have been able to tell the complete story of the family and she believes they are bowing out on a high.
She told RadioTimes.com: "We had an amazing time and we were so lucky that we were able to tell their story and to finish it off and to round it off in the way that we did, and it feels very complete, and we loved it.
"And I think this series - I really think it's the best yet. Everything was thrown at it because we knew it would be the last, so I'm really excited for everyone to see it."
And while Louisa's affair with Spiro (Alexis Georgoulis) came to an end at the end of series three, the 42-year-old actress teased that may not be the end of the plot.
She said: "Spiro and Mrs Durrell, yeah - their friendship has to - well we'll have to wait and see what happens at the end of the series."