Jennifer Garner channeled her high school self to help ring in fellow actress Reese Witherspoon’s 43rd birthday on Friday.

Garner, 46, took to Instagram to share a photo of herself dressed in a marching band uniform and playing the saxophone.

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“Many moons ago, my high school marching band played this song for homecoming. Today I play it for my boo, @reesewitherspoon. ♥️We have a groovy kind of love.♥️ Happy birthday, Lady,” she captioned the post.

“Hey, you still got the vibrato going. Nice!” one fan wrote in response.

“Marching band is awesome,” another said.

“If I didn’t adore you enough, this takes it to a new level!” a third commented.

Garner wasn’t the only celebrity to wish Witherspoon a happy birthday. In fact, some of Witherspoon’s fellow “Big Little Lies" costars -- Zoe Kravitz, Nicole Kidman and Laura Dern -- also paid tribute to the actress.

“I mean honestly. how happy are we all about @reesewitherspoon being born? This day should probably just be a national holiday,” Kravitz wrote.

“You deserve all the love and hugs in the world. Wishing you a happy happy happy birthday beautiful woman. Love being on this journey of life with you,” Kidman said.

“Today is one of my favorite holidays. It’s Celebrate Magic Day, otherwise known as Reese’s birthday. Deep, powerful, true and badass beyond measure,” added Dern.

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Others, such as talk show host Ellen DeGeneres and model Cindy Crawford, also wished the star well on her birthday.

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“For my birthday I just want all the cake, all the flowers and all the candy... is that too much to ask?! Thank you for the sweet wishes, feeling like one very lucky lady,” Witherspoon later wrote in part on Instagram.