IT'S OFFICIAL: Donald Trump picks Mike Pence as his running mate

Donald Trump announced on Twitter Friday that Mike Pence will be his running mate.

"I am pleased to announce that I have chosen Governor Mike Pence as my Vice Presidential running mate," Trump tweeted. "News conference tomorrow at 11:00 A.M."

The presumptive Republican nominee made his announcement on Twitter after postponing his planned unveiling of the selection in New York that was supposed to take place Friday. Trump delayed the event after the horrific terror attack in Nice, France, where at least 84 people were killed.

"In light of the horrible attack in Nice, France, I have postponed tomorrow's news conference concerning my Vice Presidential announcement," Trump tweeted.

Pence, the Indiana governor, issued his own statement late Thursday, saying "This attack is a horrific reminder of the threat facing Western civilization."

It was widely reported Thursday that Pence would be the choice, edging out former House Speaker Newt Gingrich and New Jersey Gov. Chris Christie. However, Trump told Fox News Thursday night that he hadn't "made a final, final decision" yet.

Pence is a former congressman who had been called a "rising star" among conservatives. He chose to run for governor of Indiana in 2012 rather than seek the Republican nomination for president, and was rumored to be considering a 2016 bid for the White House. He's currently locked in a reelection race for the governorship that he will have to drop out of. In Indiana, a candidate cannot seek the governorship and the vice presidency simultaneously.

Pence would give Trump credibility with social and movement conservatives and could help him gain an edge in what could be a close race in Indiana and throughout the Rust Belt - a stretch in which Trump must perform well.

One of Trump's closest competitors for the Republican nomination, Sen. Marco Rubio of Florida, called the selection a "great pick" shortly after on Twitter.

"@realDonaldTrump Great pick," he posted. "@mike_pence is rock solid."

Presumptive Democratic nominee Hillary Clinton's campaign wasn't as high on the selection as the Florida Republican.

"By picking Mike Pence as his running mate, Donald Trump has doubled down on some of his most disturbing beliefs by choosing an incredibly divisive and unpopular running mate known for supporting discriminatory politics and failed economic policies that favor millionaires and corporations over working families," John Podesta, chair of Hillary for America, said in a statement released by the campaign.

Pamela Engel contributed to this report