OK! EXCLUSIVE: Miley Cyrus — Moving Too Fast?

Miley Cyrus is so in love with co-star Liam Hemsworth that she's planning to marry him — even though she's only known him 10 months!

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"She's convinced she'll spend the rest of her life with him," says a source about the teenager's surprising determination to get married this year. "She's talking about a wedding as soon as she turns 18. She's even asked her mom if she can wear her wedding dress."

OK! NEWS VIDEO: MILEY CYRUS CHATS ABOUT THE LAST SONG

"He is awesome," Miley gushed about her 20-year-old beau during an appearance on Jimmy Kimmel Live. "We hang out almost every day. He's almost become like my best friend."

OK! GALLERY: MILEY LOVES (A LOT) ON LIAM AT THE LAST SONG PREMIERE

In fact, she's so serious about Liam that she even flew out to Australia to meet his family and Liam's met the Cyrus clan too!

"The whole family are great," he tells OK!. "They're really good people."

OK! NEWS: MILEY CYRUS SAYS LIAM HEMSWORTH IS HER FIRST SERIOUS BOYFRIEND

But is their relationship too much, too soon?

FOR MORE ON MILEY'S FAST MOVING RELATIONSHIP AND WHAT HER PARENTS THINK, PICK UP THE NEW ISSUE OF OK! — ON SALE EVERYWHERE THURSDAY!