Jennifer Garner can't help but wonder if the star has a secret admirer after sharing an extravagant mystery gift she received for her birthday, and it seems she's in the dark about who the sender is too.MORE: Jennifer Garner left overwhelmed by Katie Couric's surprise in latest videoThe actress turned 50 on 18 April and received quite a few shocking surprises and sweet messages, but the last gift she shared might be the most jaw-dropping, and elusive, of all.She left fans on the edge of their seats as she took to Instagram to reveal the gift, simultaneously asking the sender to reveal themselves.WATCH: Jennifer Garner works up a sweat in intense videoMORE: Jennifer Garner shares heartfelt message to her children ahead of her birthdayThe impressive present, a plane flying a banner with a birthday message across the sky, appeared presumably over Jen's backyard on the day of her birthday, but the only thing missing from the banner was who had coordinated the surprise.The message read: "Happy bday JG," a red heart in between, and then: "This is 50."She shared a video on Instagram Stories of the plane flying through blue skies above towering trees, admitting her joy over the gift as well as confusion over who it was from. The impressive surpriseThe suspenseful clip was captioned with: "Okay, c'mon now.