Jennifer Garner surprised by childhood crush Donny Osmond for her 50th birthday

Jennifer Garner celebrated a landmark birthday Sunday — the “13 Going On 30” star turned 50!

But as she revealed to her fans and followers on Instagram a couple of days before, she got the party off to an early start thanks to a surprise from former teen heartthrob Donny Osmond.

In the video clip Garner shared Friday, she can be seen sitting in a restaurant and looking shocked as she watched a personalized message that featured Osmond singing a birthday song to her.

But the exciting moment was just getting started.

Before she had a chance to thank the loved one who ordered the Blue Mountain greeting, she heard the singing continue — from right behind her. Garner jumped up and hugged Osmond and then took a moment to admire the birthday cake he brought along, which read, "13 Going On 50! Love Donny!"

"My first (pre)birthday surprise was a doozy— the one and only, legend in his own time, object of my childhood adoration and devotion— @donnyosmond showed up to knock my purple socks off," Garner wrote in a caption alongside the clip.

The musical moment in the video continued even after Osmond, 64, took a seat alongside the birthday gal, as he joined her in an impromptu performance of some of his past hits, including his 1975 cover of "Make the World Go Away."

"He took an hour and a half of his day to sit with me, sing my favorites, and to give me a master class on how to be a class act," Garner continued. "Thank you, Donny."

She also threw in a shoutout to Osmond's former onstage partner, sister Marie, as well as one for his wife, Debbie.

On Osmond's own Instagram page, he shared Garner's video, too, along with a message of his own.

"Surprising fans is one of my favorite things to do, so when I had the opportunity to surprise the lovely @jennifer.garner for her 50th birthday, I was overjoyed," he wrote. "Thanks for letting me celebrate with you! Next time you’re in Vegas, come see me at @harrahsvegas so you can be my special guest on stage. ???? "

Back on Garner's post, the comments that followed the cute clip were filled with birthday wishes from fans and her celebrity friends, including a couple of celebrities who seemed envious of her moment with Osmond.

"This is unreal," Gwyneth Paltrow wrote.

And Rita Wilson chimed into say, "I seriously think this is the best surprise that could ever be! The joy!!!"