Kate Upton has accused Guess co-founder Paul Marciano of sexual harassment, saying that she was groped during a photoshoot she did for clothing company when she was 18 years old and was just starting out in the modelling industry.

Speaking to Time Magazine, the American model alleged Marciano of "forcibly grabbing her breasts and feeling them." When she pushed him back, he allegedly said, "I'm making sure they're real."

The 25-year-old said she tried to stop him from touching her inappropriately but he continued to do so in a "very dominating and aggressive way" throughout the photoshoot.

"[Paul Marciano] was grabbing my thighs, my arms to pull me closer, my shoulders to pull me closer, my neck, my breasts, and smelling me," she told the magazine.

Upton added, "He then told Yu Tsai [photographer] to leave us alone. I was able to send a quick text to Yu Tsai asking him to stay. He did, but that did not stop Paul's constant grabbing. I was extremely shaken, surprised and scared."

Upton claims Marciano allegedly kissed her before asking her if he could join her in her hotel room, but she declined.

This, however, did not stop there as Upton claims that again after the next photoshoot with Guess, Paul started calling her asking to come up and see how her room was, but she again refused. Upton said she was so terrified that she locked herself in her room and turned off her phone.

"All I could think was if he was able to get into my room it would not be good," she said, adding the next day she learnt that she was fired from the shoot because someone from Guess told her agency that she had gotten fat.

Upton said Tsai told her that he would look after her after she told him how scared she was because of Marciano's advances.

She said Marciano was constantly texting and telling her that "he wanted me to change in front of him so he could see my naked body getting into his clothes. He asked if I thought of him when I was posing sexy on set."

Upton claimed Marciano's behaviour became more aggressive when she worked with photographer Ellen von Unwerth for a campaign. After the completion of the campaign, Upton said Marciano wanted to take her to dinner but von Unwerth insisted on coming with them. Marciano refused and Unwerth allegedly said, "Well if I'm not going, Kate's not going."

Ellen von Unwerth does not recall the particular incident but supports Upton, a representative of the photographer told the magazine.

Calling Upton's accusation "absolutely false" and "preposterous", Marciano said he supports the #metoo movement but 'will not let allow others to defame me and tarnish my reputation".

"I have never touched her inappropriately. Nor would I ever refer to a Guess model in such a derogatory manner," he said. "I have pledged to Guess and its Board of Directors my full support and cooperation with a fair and impartial investigation."

Paul Marciano
Paul Marciano at an event (File photo) Emma McIntyre/Getty Images