Plaid Cymru AM Mohammad Asghar has crossed the floor to join the Conservatives in the Welsh assembly.
The defection was announced by Welsh Conservative leader Nick Bourne and Shadow Welsh Secretary Cheryl Gillan.
Mr Asghar, the assembly's only ethnic minority AM, said he felt "out of tune" with Plaid policies, in particular its desire for an independent Wales.
Plaid Cymru said his decision was a "shock" and called for him to be "honourable" and resign his seat.
It is the first time an AM has left one party to join another, although others have sat as independents after resigning or being expelled from their own parties.
Mr Asghar was elected as a regional AM for South Wales East in 2007.
Joined by the Conservative group at a news conference, he said he had "felt out of tune with the views and policies of Plaid Cymru" and "believed in the royal family and one United Kingdom".
"My politics are very much in line with wanting a stronger Wales within a successful United Kingdom," he said.
"I believe that the Welsh Conservative Party in the national assembly, led by Nick Bourne, reflects my beliefs.
"I am also attracted by the caring Conservatism and policies for change put forward by David Cameron and the Conservative Party at Westminster.
"I very much look forward to playing an important role in the shadow team in the national assembly and to helping to shape the policies for the Assembly elections in 2011," said Mr Asghar.
Asked why he had stood for Plaid Cymru when he was opposed to independence for Wales, he said his voice had been that of "a little parrot in a jungle", with little chance of changing Plaid's stance on the issue.
Mr Asghar was originally seen as a political tool by Plaid Cymru:
"We were very proud of the fact that in campaigning hard for Mohammad Asghar's election in 2007 that Plaid Cymru ensured the first ever assembly member from the black minority ethnic community."
... Now there appears to be sour grapes:
"It is has come as a shock that he has now decided that he shares the same values as those held by the Conservative and Unionist party." Plaid Cymru assembly group chair Dai Lloyd said it would be wrong for Mr Asghar to remain in the assembly as a Conservative. "We now call on Mohammad Asghar to take the honourable decision to resign his seat as a Plaid Cymru AM," Mr Lloyd said. "The people of the South Wales (East) region did not want a second Tory AM to represent the area - they elected a Plaid Cymru AM. "Mr Asghar does not have the political mandate to sit in the assembly as a Conservative member..."
Hat-tip to the Welsh Conservatives and Mr Asghar for pulling that one out of the hat, and on the day that Rhodri Morgan tenders his resignation as First Minister.