SEE ALSO: NU'EST Aron and BTL Joel Urge K-Pop Fans to Respect this Artist's Legacy who Paved the Way for Modern Idols

The parents took the twins on a family outing to Namsan for their 500th day, and Lee Hwi Jae, Suh Un, and Suh Joon celebrated the special day by wearing matching fedoras.

They also rode a cable car together, which Lee Hwi Jae introduced to the twins, saying, "Twins, this is Namsan. Become a high person [person of high position or character like this mountain]." As soon as the cable car started to swerve a bit, he shared, "What is going on! This is scarier than I thought," bursting his strong, fatherly image for a moment. Lee Hwi Jae and his wife were also surprised at how well-behaved the boys were sightseeing, making them realize how much they've grown up.

Stay tuned for their family outing this Sunday!