Jennifer Garner plays A Groovy Kind of Love on the saxophone for Reese ...

Jennifer Garner has no shame when it comes to wishing her best pal the happiest of birthdays.

The 46-year-old star took to Instagram to bust out a little tune on the saxophone for her friend Reese Witherspoon on her 43rd birthday.

Garner was dressed in a full marching band uniform, hat and all, as she showed off her musical talent.  

Happy birthday! Jennifer Garner dressed in a full marching band costume and busted out A Groovy Kind of Love on her old saxophone as a birthday treat to friend Reese Witherspoon on Friday

Happy birthday! Jennifer Garner dressed in a full marching band costume and busted out A Groovy Kind of Love on her old saxophone as a birthday treat to friend Reese Witherspoon on Friday

'Many moons ago, my high school marching band played this song for homecoming,' Garner penned in an Instagram caption.

'Today I play it for my boo, @reesewitherspoon. ♥️We have a groovy kind of love.♥️ Happy birthday, Lady. #bandgeeksarethebestgeeks #havethebestday'

The Alias actress then proceeded to play a slightly off-key rendition of the 1988 Phil Collins hit, A Groovy Kind of Love.

The song was first released in 1965 by The Mindbenders. 

Committed! Garner even wore the classic marking band hat, complete with a giant plume of feathers

Committed! Garner even wore the classic marking band hat, complete with a giant plume of feathers

'Many moons ago, my high school marching band played this song for homecoming,' Garner penned in an Instagram caption.

'Today I play it for my boo, @reesewitherspoon. ¿¿We have a groovy kind of love.¿¿ Happy birthday, Lady.'

'Many moons ago, my high school marching band played this song for homecoming,' Garner penned in an Instagram caption. 'Today I play it for my boo, @reesewitherspoon. ♥️We have a groovy kind of love.♥️ Happy birthday, Lady.

Performer! Jennifer got totally in character as a 'band geek' as she performed the song, albeit slightly off key

Performer! Jennifer got totally in character as a 'band geek' as she performed the song, albeit slightly off key

Jennifer performed the tune as best she could whilst wearing a giant hat with a big feather plume.

She even held a note extra long so she had time to turn the page of music notes.

Jennifer Garner and Reese Witherspoon are two of Hollywood's closest A-list best friends.

The long time pals often showcase their close bond on social media. 

Pals! Reese and Jennifer have been the best of friends for a long time (pictured here in 2015)

Much love: The besties frequently show off their bond on social media (pictured in 2006)

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