Harris played for Leeds before his move to rugby union

Harris, 28, was unveiled as a Bull on Thursday, before Leeds claimed they had first option on their former captain.

However, the Rugby Football League has accepted Bradford's move after checking with its lawyers and the Rhinos are now threatening to take the matter further.

"We are grateful to the RFL for its acceptance of Iestyn's registration," said Bradford chairman Chris Caisley.

"Whilst it was obvious that Iestyn is a contracted Bulls player there was a lot of misinformation being disseminated which clouded one very simple question: Which club had Iestyn signed a rugby league contract with?"

We will now be taking legal proceedings Gary Hetherington Leeds chief executive

"As far as we are concerned that aspect of the matter is closed, although we are looking into the very serious associated matter of the defamatory comments made of our club yesterday by the chief executive of the Leeds."

Rhinos chief executive Gary Hetherington was resigned to losing Harris, but vowed to take legal action.

"We have learnt that a player contract has been lodged with the RFL to register Iestyn," he said.

"He will not, therefore, become a Rhinos player despite his contractual obligations to do so. We will now be taking legal proceedings."

Bradford believe they have pulled off a major coup by getting Harris to sign a four-and-a-half year contract.

He left Leeds three years ago in a high-profile move to rugby union, turning out for Cardiff at club level and featuring for the Welsh national side.

Bradford are a club I've got a lot of respect for, they play an exciting brand of football Iestyn Harris

He also played in the Rugby World Cup in Australia, but there was always speculation he would return to league.

Speaking at a news conference on Thursday, Bulls coach Brian Noble enthused: "We should be banging the drums and beating the gongs.

"We've got one of the best back."

Harris added: " I'm very excited about it. I've enjoyed my time in Wales and in rugby union but I felt it was the right time for me and my family to return.