Diane Kruger rarely gets it wrong on the red carpet, as she proved once again during The Host's premiere in L.A. March 19. Walking hand-in-hand with longtime love Joshua Jackson, the German actress sizzled wearing a black Thakoon dress featuring sheer side panels and and intricate beaded embellishments.

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The 36-year-old fashionista -- who joined costars Max Irons, Saoirse Ronan and Jake Abel for group pictures -- completed her look with metallic Jimmy Choo shoes and Stephen Webster jewels. "I love the idea that because the aliens have protected our world. It's peaceful and people wear white," Kruger told reporters of Twilight author Stephenie Meyers' adapted sci-fi click, in theaters March 29. "I thought that white, that purity was pretty cool."

The star, who play's the film's villain, then joked that she selected her sideboob-baring LBD because she was "rebelling against the white!" Kruger and Fringe's Jackson, 34, "looked very cuddly and in love," an onlooker tells Us Weekly. "Diane stared at Josh lovingly and seemed genuinely happy."

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At the film's afterparty, held at Lure Nightclub, Jackson was visibly excited to see his girlfriend when she arrived at 10:15 p.m. "He seemed to be beaming with pride over her great work in the film," a partygoer reveals. "He gave Diane a huge, romantic kiss at the table after hugging her and congratulating her. Josh couldn't have been more supportive and sweet."

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Even when Kruger chatted with friends and costars, she was never "more than a few steps away from Josh," the partygoer notes. "The couple stayed close the whole night and constantly made eye contact to check in while talking to other people."

This article originally appeared on Usmagazine.com: Diane Kruger Flashes Sideboob in Sexy LBD at The Host Premiere, Packs on PDA With Joshua Jackson