The Jennifer’s Body star donned the oversized bucket hat during an appearance at the Audacy Beach Festival in Fort Lauderdale, Florida.
The headgear completed a Barbie-core look comprising of hot pink crop top, bubblegum pink cargo trousers, and pink stilettos.
Fox, 36, attended the festival to support her fiancé Machine Gun Kelly during his performance.
Kelly also wore an outfit that turned heads at the event, as he opted for a contrasting all-black look.
He wore a mesh long-sleeved top and black trousers covered in rhinestones, a bedazzled belt and a spiked silver choker.
Fox became engaged to the 32-year-old singer in January, less than two years after separating from her ex-husband Austin Green.
The pair were first linked in May 2020, when they met on the set of the movie Midnight in the Switchgrass.
In an Instagram post, Fox revealed that Kelly had proposed to her under a banyan tree, where they “asked for magic” and “drank each other’s blood”.
She wrote: “We were oblivious to the pain we would face together in such a short, frenetic period of time. Unaware of the work and sacrifices the relationship would require from us but intoxicated off of the love. And the karma.
“Somehow a year and a half later, having walked through hell together, and having laughed more than I ever imagined possible, he asked me to marry him.”
In April this year, the Transformers star said she believed she “manifested” Kelly to her life.
In an interview with Glamour UK, Fox said: “[Kelly] is literally my exact physical type that I’ve been manifesting since I was four.
“I’m also four years older than him. So, I think I made him. My thoughts and intentions grew him into a person that he is, who knows what he would’ve looked like or been like if it wasn’t for me.”
Fox shares three children, nine-year-old Noah, seven-year-old Bodhi, and five-year-old Journey with Green, to whom she was married for nearly 10 years.