The 32-year-old actress voiced her love for LaBeouf on Thursday's episode of Watch What Happens Live while confirming their past fling.
"Um, I mean, I would confirm it was romantic," she told host Andy Cohen. "I love him. I've never been really quiet about that. I love him."
Fox agreed with Cohen describing her relationship with LaBeouf as an "on-set romance that didn't go anywhere afterwards." She also okayed fellow guest Tyra Banks characterizing it as a "showmance."
Transformers opened in theaters in 2007. Fox returned to star with LaBeouf in the 2009 sequel Transformers: Revenge of the Fallen, but was subsequently fired from the franchise by director Michael Bay.
"We made up," Fox said of her relationship with Bay today. "Michael and I are really good. I get invited to his Christmas parties. We're BFFs."
The actress said she's open to reprising her Transformers character, Mikaela Banes, as a cameo in future films.
"I would for a cameo or something like that," she said. "I think that franchise has probably moved so far into a different universe with different actors that it probably wouldn't make sense. But I'm not against it."