ABC News' Michael Falcone reports:

Donald Trump will endorse Mitt Romney in Las Vegas on Thursday, sources familiar with the decision tell ABC News.

A political aide in Trump's office spoke directly with Mitt Romney by phone last night before Trump's private plane took off from New York City to Las Vegas.

The call, sources say, was to inform Romney of Thursday's endorsement, which will take place at a 12:30 p.m. event at the Trump International Hotel on the Las Vegas strip.

A contracting company used by the Romney campaign has been setting up for the event since Wednesday night.

Sources familiar with Trump's thinking said that earlier reports by several news organizations of a Gingrich endorsement were inaccurate.

"I have no idea what the Donald is going to do," Gingrich told reporters on Wednesday, adding that he had not spoken to Trump in weeks.

Ever since Trump decided not to run as a Republican candidate last spring, members of his team indicated that if Trump was going to endorse, he wanted to pick a winner. Evidently, the real estate and reality television mogul, has settled on Romney as that candidate.

In an interview on "Good Morning America" earlier this week, Trump told ABC's George Stephanopoulos that he was still deciding between Romney and Gingrich.

"I'm friendly with both. I respect both," he said. "I like both. They both want my endorsement.  We'll see what happens but, in a very short time I'll be making an endorsement."

Trump's endorsement of Romney comes on the heels of multiple discussions between members of Romney's team and Trump's office over the past few months. These conversations took place at the highest levels of the Romney campaign apparatus, including campaign manager Matt Rhoades.

ABC News' Jennifer Wlach, David Muir, Jonathan Karl and Jake Tapper contributed reporting.