Kang Dong Won recently praised his co-star Song Hye Kyo on her work in the film "My Palpitating Life."

Not only is she a good actress, he said at a recent press conference, but she is also an excellent student. He taught her how to swear and she surprised him with her mastery of those curse words.

"You can hear Song Hye Kyo's tough swear words in this film," he said. "Audiences will also get to see the easygoing and wild side of her as well."

Kang Dong Won has worked with some talented female co-stars but none of them have mastered the art of swearing as well as Song Hye Kyo."

"She swore the best out of all the actresses I've seen," he said. "I can only think of Song Hye Kyo when it comes to swearing, making me forget all other actresses who swore in previous projects."

Song Hye Kyo said that it was not the first time that she heard people swear so that gave her an advantage.

"I have many people who are good at swearing around me. So I also learned it from them. Kang Dong Won also uses the dialect from Gyeongsang province and that has its own curse words as well. So I mixed that in as I learned how to swear."

But there's always more to learn.

"Song Hye Kyo has the potential to become the best student in swearing," said her co-star. "I hope that she will mix in some English words too when she acts in the future."

Talking that way did not come easily to the actress.

"The director really wanted me to swear realistically," she said. "But at first, I felt awkward because I wasn't used to swearing. But then later on I wanted to hurry up and finish it so I think I swore out of frustration."

It's the second time the actors worked together. They are both represented by the same agency and previously co-starred in "Love For Sale," a film also known as "Camellia."

"My Palpitating Life" is a film adaptation of a bestselling novel about a couple, whose son has progeria, a disease that causes him to grow prematurely old.

Song Hye Kyo also praised Kang Dong Won's acting in the film, saying he is passionate about his character.

The two have remained friends since they worked together the last time. The fact that they spend time together in real life makes his performance all the more impressive, she said.

The film "My Palpitating Life" is set to premiere on Sept. 3.