The actor in a Wales Tourist Board poster

The news has mystified people living in his south Wales home town of Port Talbot and there have even been calls for him to be stripped of the freedom of the town.

But, the star's US spokesman said: "He has been here a long time and it seems like the right thing to do."

Sir Anthony, 62, had to undergo an FBI background check, an interview with immigration officials and pass a test on his knowledge of America.

He also pledged to renounce his British ties.

A British Consulate official in Los Angeles confirmed that he could continue to use his title in the UK, but it "is not appropriate to use the honorific form in America".

Robin Gwyn of the Wales Tourist Board

The Oscar-winning actor has never made a secret of his preference for life in the US.

In the 90s, Hopkins became one of the most bankable and famous faces in films and for the past 20 years he forged his career in the US.

As Nixon he was cast as one of the most famous Americans of the 20th century.

But as Hollywood made him one of their own, his connections with Wales appeared to grow stronger.

Sir Anthony gave �1m to save Snowdon for the nation, and played a big part in promoting Wales abroad.

But the Wales Tourist Board maintained that his decision to become an American citizen was not a snub.

Hopkins' home town of Port Talbot

"It is not a matter of rejection but a matter of Sir Anthony embracing American citizenship," said spokesman Robin Gwyn.

"That is where he lives, that is where he earns his living.

"He has never denied his Welsh roots, in fact he has gone out of his way to speak publicly and extol the virtues of areas like Snowdonia."

But the residents of his home town of Port Talbot - where Sir Anthony was the son of the local baker - are not so forgiving.

Many have accused him of forgetting his Welsh roots.

Resident Glanville Mills, 67, said: "Anthony Hopkins is a local boy - it is disgusting what he has done.

"He has lost touch with his roots and should be ashamed of himself."

But the strongest response came from Assembly Member Gwenda Thomas.

She is calling for the Freedom of the Borough of Port Talbot - granted to Sir Anthony four years ago - to be removed.