Gong Yoo, 47, taken aback by 20-year-old fan's marriage declaration: 'Aren't you more like a daughter?'

Actor Gong Yoo, 47, was reminded of just how wide the age gap is after a 20-year-old fan declared she wanted to marry him.

In Sunday's episode of tvN's "Guardian: The Lonely and Great God" 10th Anniversary Travel, cast members Gong Yoo, Lee Dong-wook, Kim Go-eun and Yoo In-na gathered to share fan letters and stories.

"Guardian: The Lonely and Great God," which aired on tvN from 2016 to 2017, follows a goblin (Gong Yoo) cursed with immortality who, after nearly a thousand years of wandering, falls in love with a high school student named Eun-tak (Kim Go-eun). The drama was a major hit, becoming the first cable drama to surpass a 20 percent viewership rating.

One fan wrote that she had watched "Guardian: The Lonely and Great God" from start to finish 40 times between middle school and high school, and that she had genuinely believed a goblin ajeossi would appear holding a buckwheat flower bouquet when she reached her senior year of high school, just like in the drama.

Now a first-year university student, the fan quoted a line from the drama to confess her feelings to Gong Yoo: "Ajeossi, I love you. I'm going to marry you, ajeossi."

Gong Yoo initially responded with an enthusiastic "Wow, tell her to come," before catching himself: "Wait — but isn't she more like a daughter to me?" The exchange drove home just how much time had passed. When "Guardian: The Lonely and Great God" first aired, Gong Yoo was 37; a decade has gone by since.

Yoo In-na quipped, "Oppa is 949 years old in the drama anyway — does age even matter?"

Gong Yoo drew a line, saying, "Age is just a number, but she still has her whole future ahead of her, so I feel a little sorry. That's why I think the distance we have right now is just right."