"Not her. Not her posture, profile, poses. No sir, no way, no how," one Twitter user claimed, while another added: " … hair colour and hair parting wrong, blouse wrong, jacket collar wrong, logo on sunglasses missing on double … it defo ain't her."
Others pointed out the supposed "body double" appeared to be larger than the 48-year-old with radically different facial features.
"It's a body double that weighs a good 20lbs [9kg] more. You can see it in the round face and the 'tummy'. Hair is a totally different colour and the hairline isn't the same," one said, while another posted: "No way, look at the face, it's fuller, Melania has high cheek bones" and another said: "Look at that profile. It's not her."
Some Twitter users even claimed the body language was all wrong, with the woman in the film coming across as more confident and assertive than Mrs Trump.
"This is not Melania's body language," one posted, with another adding: "This lady steps forward and gives vigorous handshakes. Not Melania!"
Some argued the "body double" was a "paid off model" while others were convinced it was a bodyguard stepping in to play the First Lady or even a "clone" of the real thing.
Many compared photos of Mrs Trump taken earlier that day to the image in the video, claiming the pair must have switched places at some point.
Of course, the body double claims are nothing new, with the rumours first surfacing in October last year when actor and comedian Andrea Wagner Barton posted her theory on Facebook.
And last month speculation was reignited when pictures of a very different looking FLOTUS, who was in Brussels for the NATO summit, raised eyebrows.
It followed the mother-of-one's mysterious, weeks-long absence from the public eye after an announcement made by her staff on May 14 revealed she had undergone an embolisation procedure to treat a kidney condition, which was described as benign.
She remained in a military hospital for five nights before returning to the White House on May 19 to recover, and wasn't seen for almost a month.
Her absence sparked endless rumours, with some believing her illness was used as an excuse to cover up the fact she had moved back to Trump Tower in New York with 12-year-old son Barron, or had undergone a facelift.
According to the popular conspiracy theory, Mrs Trump has a body double who takes her place at public events at certain times, and it has been fuelled by her penchant for sunglasses, clothing and accessories that often cover part of her face.
Those who believe in the theory cite the First Lady's changing appearance as "proof", while some have also pointed out a secret service agent with an uncanny resemblance to Mrs Trump.
