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President-elect Donald Trump tweeted Monday evening that he would announce his nominee for the secretary of state position on Tuesday.

Two sources close to the transition told Fox News late Sunday that ExxonMobil CEO Rex Tillerson would be the pick, apparently putting an end to one of the biggest political guessing games since Trump's election victory over Hillary Clinton. However, the sources warned that nothing was official until the president-elect announces it.

EXPECTED TILLERSON PICK LATEST BLOW FOR DEMS' EXXONMOBIL SHAME CAMPAIGN

Trump's search for America's top diplomat had been carried out in highly public fashion. Speculation focused on Sen. Bob Corker, R-Tenn., who heads the Foreign Relations Committee; former New York City Mayor Rudolph Giuliani, who removed himself from contention for a Trump administration post last week; former U.S. Ambassador to the United Nations John Bolton; and, most tantalizingly, former Massachusetts Gov. Mitt Romney, once a vocal Trump critic.

Late Monday, Romney indicated that he had not been given the job in a post on Facebook.

Trump spoke highly of Tillerson in an interview aired on "Fox News Sunday," calling him “much more than a business executive.”

TRUMP TO NOMINATE EXXONMOBIL CEO REX TILLERSON AS SECRETARY OF STATE, SOURCES SAY

“He's in charge of an oil company that's pretty much double the size of his next nearest competitor," Trump told host Chris Wallace. “It’s been a company that's been unbelievably managed, and to me a great advantage is he knows many of the players and he knows them well. He does massive deals in Russia, he does massive deals for the company. Not for himself, for the company.”

If Trump picks Tillerson, the executive is likely to face scrutiny from Republican senators, some of whom have expressed concerns about his relationship with Russian President Vladimir Putin. Sen. Marco Rubio, R-Fla., a member of the Foreign Relations Committee, tweeted strong, if thinly veiled, criticism of Tillerson Sunday.

Tillersons possible selection has also been condemned by a number of environmentalists, who have allied with Democratic attorneys general to pursue a high-profile, multi-state probe into ExxonMobil that has sputtered in recent months.

May Boeve, executive director of 350.org, called Tillerson an “unfathomable” pick, adding, "Tillerson may be a friend of Putin’s, but he’s no friend of the planet. ExxonMobil is still a leading funder of climate denial and is pursuing a business plan that will destroy our future. Tillerson deserves a federal investigation, not federal office."

The 64-year-old Tillerson began his career at Exxon in 1975 as an engineer, rising through the ranks and becoming president and director in 2004 and CEO two years later. He was born in Wichita Falls, Texas, and studied civil engineering at University of Texas.

House Majority Leader Kevin McCarthy, R-Calif., told Fox News’ “Sunday Morning Futures” that Tillerson would be a “smart pick.”

Speaking on ABC News’ “This Week,” incoming Trump chief of staff Reince Priebus also defended Tillerson as an “incredible businessman and American patriot.”

While noting a “conclusion has not been made,” he stressed that Tillerson is in the business of finding oil around the world, and said “the fact that he actually has a relationship with people like Vladimir Putin and others across the globe is something that [we] shouldn't be ... embarrassed by.”

Asked about tough questions from Republican senators, he said, “We don't have concerns about confirmation.”

Should he become America's top diplomat, he will have a pay cut and complicated financial situation to sort out. Tillerson reportedly makes more than $40 million per year and owns more than $100 million of stock in a company that has holdings and dealings throughout the world.

Fox News' Serafin Gomez and FoxNews.com's Adam Shaw contributed to this report. The Associated Press also contributed to this report.