President Obama was required to take the oath once more at the White House because of a word being said out of sequence as thousands watched on when he was sworn in for the first time.
Chief Justice John Roberts, who first administered the oath in 2009, administered it again to the US leader the following day in front of reporters and members of staff.
During the initial ceremony, Mr Roberts accidentally switched the word order of the oath and said: "I will execute the office of president to the United States faithfully," instead of, "I will faithfully execute the office of president of the United States."
Barack Obama had to take his oath once more after the mistake
The President, who had interrupted Mr Roberts by prematurely starting the oath, then repeated back the line as it had been said.
"We believe that the oath of office was administered effectively and that the president was sworn in appropriately yesterday," press secretary Robert Gibbs told reporters at the time, quoting a statement from White House counsel Greg Craig.
"But the oath appears in the constitution itself and, out of an abundance of caution, because there was one word out of sequence, Chief Justice John Roberts will administer the oath a second time."
Donald Trump's Action Plan
Thu, January 19, 2017
What follows is Donald Trump's action plan to 'Make America Great Again' within the first 100 days of Presidency.
1 of 10
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Reuters reported that Mr Obama joked with reporters that he wanted to do it again for fun.
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"We decided, you know, that it was so much fun!" he said, before Mr Roberts asked him if he was ready to take the oath.
"I am. We're going to do it very slowly," the President replied before he raised his right hand and the oath was administered in the right order.
Donald Trump, who was criticised for his “temperament” during his election campaign, is set to become America’s 45th president.
The inauguration event is due to start at 5pm UK time.