Ioan Gruffudd (right) Matthew Rhys are the best of friends

Rhys - who appears in a new production of Under Milk Wood which opens in Swansea on Wednesday - said his friendship with Gruffudd was still as strong as ever, having shared a home for longer than many couples remained married.

But, in an interview in The Big Issue Cymru, he added: "The reality is we don't see much of each other because of work.

"We've lived together for 10 years, but Ioan has a serious girlfriend now so I don't know how much longer it will last."

He denied there had been any tension between the two. He said: "There are no issues between us whatsoever. If there were we wouldn't still be living with each other."

The two Cardiff-born actors have been close friends since their teens, and even played a gay couple in the film Very Annie Mary.

Rhys shot to fame as Kathleen Turner's stage toyboy

Rhys - best known for his role as the impressionable Benjamin in the West End production of The Graduate - also admitted getting annoyed at directors who disliked his Welsh accent.

"Most people are accepting of my accent, but occasionally directors have said, 'Do you mind not using it?'

"And you go 'Why? Why can't he be Welsh?' I'm intensely proud of my Welshness and, although there are times when you want to test yourself and use other accents, if the accent isn't important then why shouldn't you use the Welsh one?

"There have been occasions that, just to be stubborn, I'll say 'Well why not?' and use it."

He also said that while he enjoyed film and TV work, the stage was the most exciting because of its unpredictability.

Starring role

"You do get first night nerves when you want to throw up and you think, 'Why am I doing this?' But if it goes wrong live it's such a buzz."

Rhys admitted that when he starred opposite American actress Kathleen Turner in the stage version of The Graduate, he was forced to think on his feet.

"My character, Benjamin, has an argument with Mrs Robinson's daughter and she's meant to stomp out through the door," he explained.

"But one night the door wouldn't open, so we had to start improvising. I said something like, 'I hope you've brought your overnight bag'.

"The people we saw after the show said that had been their favourite part. The audience love it when it goes wrong. They feel like they're being let in on a secret and they want to see how you will get out of it."

The 28-year-old opens at the Grand Theatre in Swansea on Wednesday night in a new production of Dylan Thomas' most famous work, directed by Michael Bogdanov.

Rhys has the coveted role, First Voice - originally played by his idol Richard Burton.

The production later moves to Cardiff's New Theatre.

Rhys is no stranger to Under Milk Wood. His most recent performance had him playing opposite his hero in a BBC Radio Four production.

The production - to be aired in November to help commemorate the 50th anniversary of Dylan Thomas' death - uses original recordings of Richard Burton's voice.

"We were sent a cast list and it had Richard Burton's name on it!" said Matthew.

"That was quite a proud day - playing opposite Burton."