After watching Matt Ryan play suave American journalist Joe O'Hara in ABC's new period drama The Halcyon, it is a shock to the system when the actor turns out to have a Welsh accent and jokey sense of humour – even if you know he's originally from Swansea and previously starred as an irreverent supernatural detective in DC comics series Constantine.

But with the help of a dialogue coach and some reluctant friends, Ryan worked hard to recreate the voice of the 1940s American radio journalist.

"I practiced my American accent on my American friends and really annoyed them," he tells RadioTimes.com. "And then when I found out I was doing this, I got the dialect coach and worked with her and I annoyed all my friends from here as well by speaking to them with an American accent all the time. I had a lot of fun doing it.

"Because it is period and he's a broadcast journalist, I was trying to figure out what his public voice is – and then his private voice as well. So with some of the broadcasts it is a little more heightened, as it was in that period. And then obviously his private voice is his own." 

Playing smartly-dressed heartthrob O'Hara also required one major change to his appearance.

"I think it was the first time I'd clean shaven properly with a razor in six years," he revealed. "I was like – 'oh god!' You forget what you look like underneath."

As The Halcyon begins, ambitious journalist O'Hara is newly arrived in London as World War Two looms over the capital. 

"He's very much on the outside and looking into this world, and so it's kind of like he's the audience's perspective in a way," Ryan explains.

"We get the introduction to this place through him and he's always there lurking in the background looking for what's going on, and ends up getting himself into trouble with the staff and the guests.

"But then ultimately he becomes entangled with all of their lives and he's really enamoured by the British people and their courage in this terrible time in the world."

"Entangled" sounds about right.

"Joe gets caught in a love triangle with Lord Hamilton (Jamie Blackley) and Emma (Hermione Corfield) throughout the show," Ryan reveals. "He makes friends and enemies."

The Halcyon continues on Saturdays on ABC Australia