The 37-year-old got candid in a YouTube video titled "Why I Don't Talk To Shia LaBeouf." She admitted that they "weren't really close" on set and she was "salty" about his rise to fame after they played siblings Louis and Ren on the Disney Channel's Even Stevens from 2000 to 2003.
"I don't know if we ever really were friends," she said. "We were co-workers."
The Cadet Kelly alum said they "had a little bit of animosity": "I always wanted him to really appreciate what I gave to him."
Romano said she didn't know much about what was going on in LaBeouf's personal life at the time.
The actress said that she was hurt when the 35-year-old won a Daytime Emmy Award for Outstanding Performer in a Children's Series and didn't acknowledge her. "He was on the podium. I was sitting there with the rest of our team, and he thanked like everybody at the table. But he didn't thank me," she said.
"I was hurt at the time, because I felt like since day one, it was him and me. It was, like, our show. But because it was so life or death for him, it was his show, and I was just like around because I was a girl," she explained.
"I wish I would have given him more time and energy and love, like a real sister," Romano admitted.
Once the show ended, the Pieces of a Woman actor became "a huge star," Romano said. "For a while, I think the ghost of who Shia was and who he became was really frustrating for me. I didn't watch any of his movies. I couldn't. I couldn't bring myself to watch them."
"So, I kind of felt a little jilted by the whole situation," she said. "Here he is, making a big old splash in Hollywood. And here I am. I chose to go to college. And there's consequences that come [with] that but, like, there was definitely an undercurrent of regret, but also an undercurrent of comparison. Sibling rivalry, if you will."
However, the Kim Possible alum does not resent the Lawless actor now: "We just went [down] completely different pathways of life."
"I guarantee if I saw him walking on the street, there would be a bond there that is undeniable," she told viewers. "When you grow up with somebody in that particular way in that particular time in your life you're bonded together. You can't help but want to see the person succeed."
When it comes to the prospect of reconnecting with LaBeouf, Romano said that she has "a very specific life, I am sober... I have a very specific time and energy I can put towards having anyone in my life," she added. " "I'm not sure how he ever felt about me, to be honest with you."
"So Shia, if you see this, know that I love you," Romano concluded the video. "I'm sorry that we didn't connect more when we were kids and I really do hope that you are taking it one day at a time."