Donald Trump has embarrassingly called Prince Charles the "Prince of Whales" on Twitter.

The US President quickly amended his tweet to refer to the royal as the Prince of Wales but not before it was seen around the world.

Trump was defending his controversial comments that if foreign governments offered his campaign damaging information against a 2020 rival that "I think I'd want to hear it".

"I think you might want to listen, there isn't anything wrong with listening. If somebody called from a country, Norway, [and said] 'we have information on your opponent,' I think I'd want to hear it."

If Trump was to do that it would be illegal under campaign finance law, as this kind of information would be considered highly valuable.

Trump took to Twitter to, ahem, clear up the matter.

"I just met with the Queen of England (U.K.), the Prince of Whales (sic), the P.M. of the United Kingdom, the P.M. of Ireland, the President of France and the President of Poland.

"We talked about "Everything!" Should I immediately call the FBI about these calls and meetings? How ridiculous! I would never be trusted again.

"With that being said, my full answer is rarely played by the Fake News Media. They purposely leave out the part that matters."

Twitter immediately had a field day with Trump's comments, with Prince of Whales trending on the social media site.

All jokes aside, Trump angered many with his comments saying he would accept "dirt" on an opponent if it was offered to him from foreign governments.

Republican Senator Lindsey Graham said "foreign influence in our elections is growing, not lessening, and we don't want to send a signal to encourage it".

"Giving you anything of value whether it be money or information on your opponent, the right answer is no," Graham said. "I think it's a mistake [by Trump]. I think it's a mistake of law. I don't want to send a signal to encourage this."

Graham was also asked about Trump's suggestion that politicians would accept foreign information in the same way.

"I can only speak for myself. I've never had a government come up to me and say 'hey, I'd like to help you in your campaign.' The answer is no. It's got to be no," Graham said.

"We need to really be clear here that we don't want parties to be hiring foreign agents and we don't want to have meetings with representatives of foreign governments trying to help one campaign over the other."