While her BFF Vanessa Hudgens is busy filming Spring Breakers down in Miami, Ashley Tisdale is having some fun in the sun on her own.

In a pic posted to her Instagram Thursday, the Hellcats star showed off her trim body and toned tush (with tan lines) in a skimpy brightly colored string bikini.

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"What a beautiful day," the 26-year-old wrote along with the photo.

In February, Tisdale made her red carpet debut with her beau of two months, Boys Like Girls lead singer Martin Johnson.

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The pair met back in 2009 when Tisdale starred in Boys Like Girls' "Love Drunk" music video; she was dating music video director Scott Speer at the time.

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"They're still going strong," a source tells Us Weekly of Tisdale and Johnson. "She's a firecracker and Martin loves that."

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