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Miley Cyrus, Liam Hemsworth

Lester Cohen/Getty Images

The man by Miley Cyrus' side won't be her dad this time.

In a true sign that she's really growing up, the erstwhile Hannah Montana will be posing on the red carpet with her boyfriend, Liam Hemsworth, for the first time during the premiere for The Last Song, E! News has learned exclusively.

Sure, Liam also plays her love interest in the film, so he'd obviously be at the Arclight in Hollywood Thursday night anyway. But, after their recent declarations of love and boyfriend-girlfriendiness, the young couple is ready for a big public debut (Robsten, take note).

"They're just so happy together that they see no reason to hide it anymore," a source tells us. "They will walk the carpet together."

Before all that, the starlet will be mentoring the remaining contestants on tomorrow's American Idol before she takes the stage herself during the results show on Wednesday.

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Maybe, down the road, these two will join our Weddings We Can't Wait For gallery! You never know!