Reese Witherspoon and Ava Phillippe
Ava Elizabeth Phillippe and Reese Witherspoon at the premiere of HBO's Big Little Lies at TCL Chinese Theatre on 7 February 2017 Getty

While young Ava is all grown-up, her actress mother Reese Witherspoon hardly shows any signs of ageing as she continues to wow fans with twinning snaps with her daughter. Most recently, though, the 41-year-old actress got social media buzzing by sharing a sweet throwback photo with her lookalike daughter.

"Happy 18th Birthday to my sweet girl @avaphillippe!" the proud mum wrote alongside the snap, which she shared with her 10.7 million followers on Instagram. Shared in honour of her daughter's 18th birthday over the weekend, the picture, however, showed a much-younger Ava with an ever-youthful looking Witherspoon.

With the exact same blue eyes and luscious blonde locks, the mother-daughter duo cut an insanely adorable figure, sending all of Instagram into a frenzy.

A fan wrote, "Can't believe Reese is 41 & her daughter is 18... Must be the prettiest youngest mom," while a second couldn't conceal surprise and added, "My god Reese, do you ever age!!"

As the birthday wishes continued to pour in, most fans and followers of the Legally Blonde star expressed excitement at seeing the lookalike pair and Witherspoon's age-defying beauty.

"You look the same all these years later @reesewitherspoon ! I saw the pic but didn't read the caption and I was like oh she must be holding a niece or a friend's kid," one Instagram user shared, while another went on to congratulate the "proud mama".

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"Wow 18 years old already...what a proud mumma...she's a beautiful gift," the fan said about Ava.

However, it wasn't just the Big little Lies actress, who sent social media into a meltdown with her daughter's pictures. Following Witherspoon's suit, even her ex-husband Ryan Phillippe shared touching throwbacks to mark his daughter's big moment, turning into an adult.

"Happy birthday, punk. I love you more than any strangers need read, but..." the Cruel Intentions star wrote sharing a bunch of old clicks from different stages of his daughter's life.

"And even though you're no longer a child, you'll always be my little girl. Happy 18th, princess," he added alongside a very cute snap showing little Ava in a pink tutu.