Miley Cyrus is rumored to be engaged to Liam Hemsworth after being spotted wearing a diamond ring on her wedding ring finger.

The 19-year-old former Hannah Montana star has posted a picture of her manicure on Twitter - revealing a big rock parked on her left hand in the process.

The couple - who have been dating on-and-off for three years since meeting on the set of The Last Song, and have a puppy called Ziggy together - also attended Muhammad Ali's Celebrity Fight Night XIII in Phoenix, Arizona, on Saturday night, where Miley was once again wearing the jewel.

While one source tells US Weekly the ring is not an engagement ring, a second insider insists a wedding is definitely in the pipeline. "They're still keeping it a big secret, but they're seriously talking marriage. Liam is crazy about her, though he hasn't proposed formally yet," an insider said.

And the news would reportedly be well received by Miley's parents Billy Ray and Tish. "The whole family loves him. They know Miley's no angel, but she's much calmer with him in her life," the source said. A rep for Miley was unavailable for comment.