The "Party in the U.S.A." singer, 19, Tweeted a photo of her left hand rocking a mysterious diamond sparkler on Thursday with the caption, "I am sooo obsessed with @jennahipp nail foundations!"
Despite the accompanying manicure-related Tweet, the focus-grabbing diamond was the obvious star of Miley's photo, sparking speculation that the singer/actress and her "" star beau could be engaged.
The gorgeous pair did nothing to squelch engagement rumors as they stepped out together for Muhammad Ali's Celebrity Fight Night XVVIII in Phoenix, Ariz., on Saturday evening, where Miley posed for red carpet photos with the rock prominently displayed on her wedding ring finger.
Miley and Liam have been dating on-and-off since 2009 and have a puppy (English bulldog Ziggy) together.
Miley recently sang her Australian boyfriend's praises at "The Hunger Games" Los Angeles Premiere, where she told Access Hollywood she's thrilled for Liam's recent success.
"I'm so excited, this year has just been amazing and Liam deserves it. There's so many people out there that I think don't even know what he's capable of and I can't wait until people see it!" Miley told Access' Shaun Robinson at the movie's premiere earlier this month.
"He loves making movies and it's not about any of the fame or anything else other than he just loves filmmaking," she added.
A rep for Miley was not immediately available for comment on the possible engagement when contacted by Access Hollywood on Sunday.
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