The 42-year-old actress dedicated a sweet post to Kidman, her "Big Little Lies" co-star, on Instagram on the actress' 51st birthday Wednesday.
Witherspoon and Kidman play Madeline Mackenzie and Celeste Wright on "Big Little Lies," which started production on Season 2 in March.
Witherspoon shared a photo of herself and Kidman on the show's set.
"Happy Birthday to this remarkable woman who I'm lucky enough to work with and call my friend. Everyday with you is an inspiration! Keep shining bright, Nicc!! @nicolekidman," she captioned the post.
Kidman also received birthday wishes from longtime friend and "Flirting" co-star Naomi Watts.
"Happy birthday to this incredible woman who has inspired, impressed and supported me for more than 3 decades. @nicolekidman I absolutely love you. #bossladies #soulsisters," the 49-year-old actress wrote on Instagram.
Kidman's husband, country star Keith Urban, serenaded the actress during his concert Tuesday at the Country USA music festival in Oshkosh, Wisc.
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Kidman shared a video of the moment Wednesday on Instagram.
"What a gift - my husband and everyone at @officialcusa Oshkosh WI singing me Happy Birthday!!!!!!" she wrote.
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