Paul Marciano insists he has "never acted inappropriately" towards Kate Upton.
The 25-year-old model-and-actress accused the Guess co-founder of sexual misconduct on Twitter last week, but the 65-year-old designer has branded the social media post "malicious and false".
He said in a statement issued to TMZ: "Ms. Upton provided no details ... She leveled this malicious and false accusation only hours before a gala event at our headquarters in Los Angeles unveiling a new Guess campaign. Ms. Upton told TMZ that 'I'm excited to tell my whole story.'
"As of today, Ms. Upton still has provided no facts, details, no dates and no circumstances to back up anything she has alleged.
"I am told that she has been working with others for some time to defame me and will claim that I groped her among other things.
"This accusation is false. I have never touched Kate Upton. I have never been alone with Kate Upton. I have never acted inappropriately towards her."
The designer went on to thank those in the fashion world who have given him their support following Kate's post.
He said: "In recent days, many models, photographers, stylists and others have reached out to express support based on their longstanding personal and professional interactions with me.
"I deeply appreciate their encouragement during this challenging time for me and my family."
Paul - who insisted he is a strong supporter of the #metoo movement - doesn't want to see his "reputation be tarnished" and has vowed to fully co-operate with investigations into his alleged conduct.
He added: "I have devoted my entire career to building a fashion company and brand that have a long and proud record of empowering women.
"I fully support the #metoo movement.
"At the same time, I will not stand by and watch my reputation be tarnished. I have pledged to the Guess Board of Directors that I will fully cooperate with a fair and impartial investigation into all the facts. 'I have complete trust and confidence that the actual facts - not unverified tweets or uncorroborated Instagram posts - will prove that the accusations against me are untruthful."
The 'Other Women' star last week slammed Guess for keeping the designer in a position of power.
She posted on Twitter: "It's disappointing that such an iconic women's brand @GUESS is still empowering Paul Marciano as their creative director #metoo (sic)"
She later reshared the tweet on Instagram and added the caption: "He shouldn't be allowed to use his power in the industry to sexually and emotionally harass women #metoo (sic)"
The 'Disaster Artist' actress' husband, Justin Verlander, also retweeted the post.
Tagged in Kate Upton