Republican presidential candidate, former Massachusetts Gov. Mitt Romney, waves to supporters at his Florida primary primary night rally in Tampa, Fla., Tuesday, Jan. 31, 2012. (AP Photo/Gerald Herbert)
UPDATE-3 P.M. - Donald Trump has confirmed that he will endorse Mitt Romney's GOP presidential bid. He says he made the decision after getting to know Romney after meeting with him several times in the past few months.
He also cited Romney's performances in presidential debates and his tough stance on China as reasons.
Trump was set to announce his support for the Massachusetts governor Thursday afternoon in Las Vegas.
He confirmed the endorsement while speaking with reporters gathered at his Las Vegas hotel for the announcement.
Trump has said negative things about Romney in the past. But he said his comments were a reflection of not knowing Romney well enough.
Trump also said he would not run for president as an independent if Romney becomes the GOP nominee.
UPDATE: Mitt Romney will receive Donald Trump's presidential endorsement Thursday, sources with knowledge of the endorsement told CNN.
Trump told news media on Monday that "I really want to endorse somebody and I'm going to be doing that over the not so distant future, and I'm going to be doing that, and if that person doesn't win, you know, we'll see what happens."
The sources of information are obviously two different ones. Check back for a definitive endorsement.
(Earlier today) LAS VEGAS (AP) — Real estate mogul and reality show star Donald Trump intends to endorse Newt Gingrich's GOP presidential bid, according to a source close to Gingrich's campaign.
Trump is set to announce his support Thursday in Las Vegas, where Gingrich is campaigning in advance of Nevada's Republican caucuses on Saturday.
Trump's backing would bring the former House speaker a blitz of media attention heading into the contest and following his defeat in Florida.
Trump announced Wednesday that he was to make news in the presidential race but did not say what it was.
Asked about the possible endorsement Wednesday in Reno, Nev., Gingrich said he had "no idea what the Donald is going to do."
"He is always interesting," Gingrich said of Trump. "And I don't know of anybody who does a better job of getting attention by announcing that he will presently announce something."
Gingrich sought Trump's endorsement at a meeting in December at the real estate mogul's Trump Tower office in Manhattan. There, Gingrich told reporters he had persuaded Trump to mentor promising children from some of New York's poorest schools.
The former House speaker had come under fire for suggesting poor children should do janitorial chores in their schools to learn the value of work.
Gingrich also agreed to appear in a Republican debate Trump was to host in Iowa in December. But other candidates, including frontrunner Mitt Romney, turned down the debate, forcing Trump to cancel.
Trump had flirted with the idea of jumping in the presidential race as a third-party candidate but ultimately decided not to.
Appearing on CBS' "Face The Nation" on Sunday, Trump praised Gingrich.
"He's got great ideas. He's very smart, he's very tough and he is a great debater," he said
The source was not authorized to speak for the campaign and spoke on condition of anonymity.