Actor Yoon Si Yoon shared for the first time a painful childhood tale of when he was instructed not to refer to his mother as "Mom."

During the end of the Aug. 10 (KST) edition of SBS's My Little Old Boy, Yoon's Mongolian trip with his mother was highlighted.

As a white-clad woman approached, Yoon greeted her affectionately as "Mom," and the studio panel was surprised, commenting on her young appearance and envying them for their impending mother-son adventure.

While enjoying the scenery of Mongolia, Yoon's mother shouted, "Si Yoon, I love you, my son." Afterward, the two were seated for an emotional talk.

READ MORE: Yoon Si Yoon Dating History: Here's How Romantic the 'You Raise Me Up' Star to His Past Girlfriends

"As soon as she became an adult, my mom had to start working because of me. She became a mother at a young age." Yoon stated.

His mom also regretted the sacrifices she made, acknowledging, "Because I became a mom so young, I don't even know when you took your first steps. I missed many parts of your growth."

She then shared a childhood memory of Yoon's. "In front of guests, I told you not to call me 'Mom'," she recalled.

Yoon recognized how much it hurt him. "As a child, that really hurt my feelings," he acknowledged, speaking of the years he couldn't correctly refer to her as his mother.

Getting choked up, his mother furthered, "I am truly so sorry to you. Even now, I feel that way," before tearing up. Yoon reassured her with compassion and warmth.

Yoon was born in 1986, and he just signed up for My Little Old Boy. He has already revealed that he lost 10 kilograms during the shoot of SBS drama Taxi Driver 3.

READ MORE: 'It's Beautiful Now' Stills: Yoon Si Yoon is Romance-Allergic Divorce Lawyer in New Drama