Gov. Chris Christie endorses Donald Trump — VIDEO

New Jersey Gov. Chris Christie offered a surprise endorsement to Donald Trump on Friday, saying there is no one better prepared to lead the country or defeat former Secretary of State Hillary Clinton should she become the Democratic nominee.

"I am proud to be here to endorse Donald Trump for president of the United States," the New Jersey Republican told reporters at a press conference in Texas. "The best person to beat Hillary Clinton on that stage last night is undoubtedly Donald Trump."

Christie is the first of Trump's former rivals for the Republican nomination to endorse the billionaire presidential candidate, who has now won three out of four primary contests and is increasingly viewed as the most likely candidate to become the GOP nominee. The endorsement gives him an establishment endorsement and once again Trump has stolen the news cycle from his primary Rubio.

Christie, who has long been family friends with Trump, pledged he would help Trump campaign for the presidency through the general election in November. He introduced Trump at a rally Friday in Fort Worth, Texas, and will also appear with him in Oklahoma City Friday evening.

The endorsement came as a surprise to the assembled press, and audible gasps could be heard as Christie walked into the room with Trump. Trump said during his Texas rally that he wanted to "keep it a secret for the people of Texas."

The source added Christie picked Trump over Cruz because of Cruz's ideological rigidity.

As for Rubio, the source said Christie's disdain for Rubio that became so evident on the debate stage was not feigned, but simply how Christie feels about the Floridian.

Senior Rubio aide Todd Harris poked fun at Trump for the endorsement.

"Gov. Christie is a very articulate guy which is probably why Donald Trump had to bring him on to his campaign," Harris said. "Clearly Donald Trump is incapable of explaining any of his ideas for the future of this country, he's incapable of explaining what's hiding in his tax return."

While Christie profusely lauded Trump during the news conference Friday, the New Jersey governor known for his similarly brash style had previously slammed Trump as an "entertainer in chief" during the Republican primary race and called Trump's plan to temporarily ban Muslims from the United States "ridiculous."

"That part is over," Christie said of the fighting between the two men during the primary race, adding that his decision to endorse Trump came down to "who is the best person to stop Hillary Clinton from getting inside the White House ever again."

He added: "There is no one who is better prepared to provide America with the strong leadership that it needs."

Trump and Christie appeared on stage together the day after a tense debate in which performance where the real estate mogul faced off against Rubio and Texas Sen. Ted Cruz. Christie and Trump took turns unloading on the freshman Florida senator, who spent the morning insulting the billionaire businessman.

"Desperate people do desperate things," Christie said when asked about Rubio's comments, adding that his remarks were the "flailing punches in the final days of the campaign."

Christie added that Trump was the one candidate who would be "strong enough to take on the D.C. establishment," which Christie said Rubio embodies.

Introducing Trump at the Fort Worth rally, Christie said Trump was the "one strong man on that stage" during the GOP debate Thursday night.

Trump went after Rubio for wearing too much makeup during Thursday's debate.

"I saw him backstage and he was putting it on with a trowel," Trump said before repeating his attack that the Florida senator chokes under pressure.

Christie, in the waning days of his own presidential campaign, had specifically targeted Rubio as not qualified for the office.

"Generally speaking, I'm not big on endorsements," Trump said, adding, "This was an endorsement that really meant a lot."

Christie said he decided Thursday to join Trump on the campaign trail.

"Yesterday morning I met with Donald and we sat and talked and he said, 'How about coming out to Texas with me?' and I said, 'Happy to do it, whenever you're ready sir,'" Christie said.

Asked about whether he would consider Christie as his running mate should he win the nomination, Trump said he didn't "want to discuss that," but added: "He's certainly got the talent."

Trump has previously said that he would pick a running mate with political experience, and not someone from the private sector like himself.

When asked about the endorsement, Cruz dodged on weighing in.

"This decision is going to be made by the voters on Super Tuesday," Cruz told Fox News' Sean Hannity in Nashville, Tennessee.