Song Joong-ki and Song Hye-kyo's relationship, despite being constantly under scrutiny by fans, was a well-kept secret that very few knew about. Actor Cho Tae-kwan, who recently revealed in an episode of MBC's 'Radio Star' that he had felt the two were dating on the sets of 'Descendants of the Sun,' apologised for talking about the top Hallyu stars.

As noted by website Allkpop, Cho Tae-kwan, also known as Jasper Cho, said, "I just answered because they asked me but I think I made a mistake. I just said it as it is but I'm sorry to the two people."

As noted by website Koreaboo, actor Cho Tae-kwan, who played Doctor Daniel Spencer in a supporting capacity in 'Descendants of the Sun,' revealed in an episode of MBC's 'Radio Star' that neither the cast nor the staff knew that their lead actor and actress were romantically entangled.

Even the director was unaware of the two dating and advised the actors, "Be more genuine and try to really like each other." Jasper says that Song Joong-ki's answer gave a hint that the two top Hallyu stars were more than just colleagues and friends.

As noted by Allkpop, he had said, "At the time, I didn't know they were dating but I heard the director telling them to really try liking each other with sincere feelings. In response, Joong Ki told him, 'We're already doing well on our own.' Now I think of it, they really were doing well on their own."

Meanwhile, K-pop group g.o.d member Park Joon-hyung, recalled how kind a person Song Hye-kyo was to him when they filmed a sitcom together. As noted by Soompi, g.o.d members Joon Park and Son Ho-young appeared as guests on the July 13 broadcast of tvN's 'Life Bar.'

Son Ho-young recalled, "When Joon Hyung was in the middle of shooting the sitcom, Hye Kyo visited us at our dorm. There were probably a lot of flies around and it was dirty and we were sleeping in our underwear, but somebody beautiful came walking towards us."

To this, Park Joon-hyung added, "Hye Kyo was in high school at the time and always came to work in her school uniform. She knew I didn't have a manager so she'd ask me to go out to eat with her. She was really kind."

Song Hye-kyo's acts of kindness are well-known. She recently donated in secret, generous amount of funds to a children's hospital in May. She has narrated a documentary on terminally children and has volunteered many times at animal shelters to care for dogs and other animals that are unwell or abandoned.

Song Hye-kyo will marry Song Joong-ki on October 31, this year.