Donald Trump is going back on his promise not to run as an independent candidate, should he not win the Republican nomination to run for President.
Mr Trump is on course to win the required number of delegates to get the nomination, but fears the party will turn on him at the last-minute and nominate one of his rivals, Ted Cruz or John Kasich.
If he runs as a third-party candidate, it would almost guarantee a win for the eventual Democratic nominee -- either Hillary Clinton or Bernie Sanders.
In September last year Mr Trump signed a pledge he would only run as the Republican nominee, but now says he is being "treated very unfairly".
"Do you continue to pledge [to support] whoever the Republican nominee is?" CNN host Anderson Cooper asked the real estate mogul at a town hall debate yesterday.
"No, I don't anymore," Trump said. "We'll see who it is."
Mr Cruz and Mr Kasich both also said they would reserve support for their own party's candidate, should it be Mr Trump.
"I'm not in the habit of supporting someone who attacks my wife and attacks my family," said Mr Cruz.
"If the nominee is somebody I think is really hurting the country, and dividing the country, I can't stand behind them," said Mr Kasich.
And Marco Rubio, who quit the campaign trail after heavy defeats two weeks ago, has asked states which have pledged him delegates not to release them to other candidates -- suggesting he might put his hat back in the ring, should no other candidate win a majority.
Mr Rubio says he wants to "give voters a chance to stop Trump", but is still "no longer a candidate".