Jenna Coleman has said it was "pretty terrifying" to play a native French speaker in The Serpent.
The actress told the Table Manners With Jessie Ware podcast that the last French lesson she had was when she was aged seven in primary school.
The BBC drama is based on the true story of how murderer Charles Sobhraj (played by Tahar Rahim) - who was the chief suspect in unsolved murders of young Western travellers across India, Thailand and Nepal - was captured.
Coleman plays his partner Marie-Andree Leclerc, who is from Quebec in Canada.
"When I read the script I was like, 'There's no way I can't do it'.
"I'm also such a big fan of Tahar as well.
"But it's like it's half French but not just French, French-Canadian.
"There's only a space of kind of a few weeks and scripts were still being tightened.
"My first day on set, the whole crew were Thai, and all the actors I worked with are actually French and I just landed in Bangkok and I was like, 'What am I doing? What is going on?'"
She said it was "pretty terrifying to be honest".
Coleman added that "so many things went wrong" with the filming of the series because of delays caused by coronavirus and scheduling.
"The shoot was supposed to take four months, it then took 13, so we all got to know each other really well," she said.
"It's so weird for me now when I see people freaked out or scared of Tahar because he could not be more opposite to that character."