She's "The Master" of the abs!

Laura Dern took advantage of the scorching hot temperatures in Los Angeles on Tuesday to hit the beach -- and show off her stealth bikini bod!

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The 45-year-old actress -- who costars in the buzzed-about new film The Master -- hit the surf with Jaya, her 7-year-old daughter with ex Ben Harper. Showing off an enviable set of abs and toned arms, the Oscar nominee wore a striped bikini top and plaid board shorts.

She and singer Harper, 42, also share a son, Ellery, 10; following a brief reconciliation, Dern reactivated dormant divorce papers back in July.

But Dern was part of a much happier romantic story this past summer: Back in July, Dern (with Ellery and Jaya in tow) dined in NYC with Courteney Cox (plus her daughter, Coco) and Justin Theroux. One of Jennifer Aniston's closest pals, Dern broke bread with Theroux shortly before he proposed to his Wanderlust costar, 43.

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"Everyone seemed to be having fun," a source adds of the dinner, which took place at Aniston was on location shooting We're the Millers in North Carolina.

This article originally appeared on PIC: Laura Dern, 45, Shows Off Hot Bikini Bod at Beach With Daughter