's 50th birthday celebration is already one for the books.

The star, who turns 50 on Sunday, got quite the surprise from legendary singer on Friday.

In a clip shared on Instagram, Garner appears to be in awe as she watches a video of Osmond, 64, singing to her for her special day. He suddenly pops up behind her to complete the tune in person.

Garner then stands and hugs him as he presents her with a cake that reads "13 going on 50," a nod to her popular film, The two go on to sing a duet together before Garner covers her face with a napkin, seemingly still in shock over the moment.

"My first (pre)birthday surprise was a doozy— the one and only, legend in his own time, object of my childhood adoration and devotion—

"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. Thank you, Donny. 💜 Hi, . ☺️ I hope to meet you someday, Debbie. ♥️," Garner added to his sister .

Garner first in May 2019 when news anchor shared of performing with The Osmonds wearing brightly-colored jumpsuits, writing, "If this doesn't get you going this morning nothing will. Long live @cher and the Osmonds."

"My number one biggest crush of all time @donnyosmond," Garner commented, along with a kissing face emoji.

Donny then responded to the actress by joking, "Miraculous that those jumpsuits didn't scare you away." But things didn't end there.

He took a screenshot of an article about their Instagram interaction and posted it to his Instagram Story. "You learn something new every day!" he wrote, referring to Garner's newly-admitted crush.

Donny continued by acknowledging Garner's appearance in and wrote, "Congrats on being featured in @people's 2019, @jennifer.garner. No beauty shines greater than a good heart."

Garner then reposted Donny's Instagram Story to her own, writing: "1st Grade Jennifer is freaking out right now."

"I still love purple socks," she added, referring to his fashion choice.