EXCLUSIVE: Miley and Liam Are Engaged!

Miley Cyrus and star Liam Hemsworth are engaged to be married after three years of dating, their reps confirm to WHO exclusively.

The rising Australian actor popped the question to US pop singer-actress Miley Cyrus in Los Angeles on May 31, in what a source describes as a “really romantic” proposal.

The Hunger Games star, 22, presented his longtime girlfriend with a 3.5-carat, cushion-cut diamond set in an Art Noveau-inspired gold band from jeweler Neil Lane.

“I’m so happy to be engaged and look forward to a life of happiness,” Cyrus, 19, tells WHO exclusively. Adds the source, “She’s so madly in love, it’s not even funny.”

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The couple met in 2009 when they co-starred in the romantic coming-of-age film The Last Song, and shared their first kiss on-screen. Despite a brief split in 2010, they’ve since shown signs they’re serious about each other: they’ve been living together in LA’s San Fernando Valley with their five dogs and both have spent time with the other’s family.

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Despite her young age—Cyrus turns 20 in November—her singer dad Billy Ray and mum Tish are “thrilled” at her happy news. They’ve “always thought of Liam as part of the family,” says the source. “They’re just so happy she’d found someone who makes her so happy.”

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Hemsworth's Aussie clan is "equally overjoyed", says a source. Having embraced their future daughter-in-law, "they are all one big happy family."

It’s a two-way street, according to Hemsworth, who was attracted to the “Party In the USA” singer for her “confidence.” The dashing 1.9m actor credits his famous fiancée for her support as his star grows in the wake of this year’s smash flick, The Hunger Games. “She embraces [my new fame]. She’s very, very happy for me,” he’s said of the former Hannah Montana starlet. “We’re always supportive of each other’s careers and we both know how we feel about each other.”

Following news of her surprise engagement Wednesday, Cyrus, took to Twitter:

As for when the loved-up young stars will walk down the isle?

The pair are in no hurry to set a wedding date, says the source. “It’s all very new for them. They’re just so in love and so happy that the can take things to the next level.”

To see and read all about Miley's stunning 3.5 carat engagement ring from the man who designed it himself, Neil Lane, click here.

For more on Cyrus and Hemsworth's engagement, including what their families think – pick up this week's issue of WHO, on newsstands Friday.