Conspiracy theorists on Twitter think Melania Trump was replaced by a body double as her husband addressed the media last week.

Twitter users say the woman standing next to President Donald Trump as he spoke on the White House lawn on Friday did not look like his wife.

"This is not Melania. To think they would go this far and try and make us think it’s her on TV is mind blowing," posted Twitter user Joe Vargas.

"Makes me wonder what else is a lie," he added.

Mr Trump spoke to the waiting media on the lawn before a trip to visit a nearby US Secret Service training facility.

Mr Vargas said the President was clearly trying to convince the media that his wife was with him during his remarks.

In a video clip, Mr Trump is heard saying: "My wife Melania, who happens to be right here, finds that subject to be of such vital importance, she’s very much involved."

Mr Vargas’ tweet racked up nearly 50,000 retweets, and #FakeMelania started trending on the social media site.

While some are convinced the woman standing next to Mr Trump was not his wife, others joked it could not be possible because the President would not be able to find another woman prepared to spend time with him.

Photos from later in the trip, where the First Lady is not wearing sunglasses, show clearly that Melania Trump was at the Secret Service facility with her husband.

(c) Sky News 2017: Melania Trump body double conspiracy theory spreads on social media