When Victorian teenager Laura Griffin saw her actor boyfriend of five years Liam Hemsworth passionately kissing the world's most famous teenager, Miley Cyrus, on the set of The Last Song, she believed he was only doing his job.

But as the 19-year-old student would soon discover, the love of her life was not acting at all — he had fallen head over heels for the Hannah Montanas star.

Even worse, Laura had to learn from friends that 19-year-old Liam was dating the teen star.

"He was my boyfriend and my best friend," Laura tells Woman's Day in an exclusive interview. "There is no other reason why we would have broken up." In the days since she found out her boyfriend had dumped her for Miley, 16, Laura has confessed on her Facebook site her "total utter regret", that she's suffering "depression of some sort", and that she has "tears streaming".

Meanwhile, the millionaire US actress is using Twitter to bask in the joy of her romance with former Neighbours star Liam. "Against all odds I fell in love," she wrote recently.

"I think I'll just sit around and eat sushi and watch Liar Liar with Liam."

Liam and Laura's paths first crossed in Year Eight at school on Phillip Island. Liam's parents had relocated their three boys, Luke, Chris and Liam, from Melbourne.

"He was the new boy at school and all the girls liked him," smiles Laura. "He was popular, a bit of a joker and made me laugh."

Just a year later, their friendship blossomed into real love. "We became inseparable. He tried to teach me to surf, we watched movies, and went shopping. Liam became more than a boyfriend, he was my best friend."