Donald Trump Jr has once again triggered massive outrage and biting remarks after "ridiculously" praising his father for standing and singing the national anthem. After being greeted with a mix of cheers and boos at the at the College Football Playoff National Championship game on Monday (8 January), President Donald Trump took to the field and stood with his hand over his heart for the national anthem.

However, footage of Trump singing the anthem has gone viral after the president appeared to mumble parts of it prompting many social media users to question whether he knew the words to The Star-Spangled Banner.

Many critics blasted Trump over the gaffe after the president spent months criticising NFL players who kneel at games in protest of inequality and police brutality in the country.

Still, amid the flurry of snarky comments and furious criticism, Trump's eldest son took to Twitter to post a photo of his dad and rave about his anthem etiquette at the game.

"And that folks is how it's done. It's not that hard. Just show some respect for your country," Trump Jr tweeted along with a screengrab of a Fox News broadcast that shows Trump with his hand on his heart during the anthem.

Twitter users were not appreciative of Trump Jr's "condescending" tweet and responded with a barrage of fiery comments.

"How what is done? Butchering the words to the National Anthem?" one person tweeted.

Another user shot back: "This is NOT how it's done. A POTUS (cough) should know the words to our National Anthem. He looked ridiculous!!!"

"Since when did it become a news alert when a president stands for the anthem?" one user tweeted.

"It would be great, if the President of the United States know the words of the national anthem. Not more, not less," someone wrote.

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President Donald Trump on field during the national anthem prior to the CFP National Championship Jamie Squire/Getty Images