Lee Bo Young and Ji Sung want to keep their wedding simple, so the guest list is limited to 200, which is on the small side for a celebrity wedding. But that doesn't mean they won't have an all-star lineup of celebrities performing.

The most recent entertainment addition is singer-actress-author Gu Hye Sun, who is most famous for her role as Geum Jan Di, the F4-defying heroine of "Boys Over Flowers."

Gu will sing a congratulatory song that she wrote and composed. The song, "It's You," is about love at first sight.

When her good friend Lee Bo Young asked her to sing at the wedding, Gu knew exactly which song she would perform.

"It was then that I realized that there was a reason for my writing this song," said Gu.

Although she gets anxious just thinking about performing, it's something she wants to do for her friend.

"I am so nervous about going on stage that if I know I have to, I can't sleep at night," said Gu. "But although I am scared, I will do my best."

Two other celebrities will perform at the couple's Sept. 27 wedding at the W Seoul Walkerhill Hotel.

One is Lee Bo Young's "I Hear Your Voice" co-star Yoon Sang Hyun. Their characters briefly dated but then went on to be good friends. On set, they also became good friends and liked to joke around with each other.

"Lee Bo Young asked me to sing 'Never Ending Story' at her wedding," said Yoon, who then went on to tease her. "She asked me to sing the song for her parents but I may or may not sing it depending on the way she acts."

Yoon Sang Hyun, who played Oska in "Secret Garden," initially wanted to be a singer but his singing career was not launched until he made a name for himself as an actor.

One other person who might sing is Kim Bum Soo of "Music Plaza." When Ji Sung appeared on his show to discuss wedding plans, he cautioned that people should not be offended if they were not invited to his wedding. Ji Sung, star of "Protect the Boss" and "Secret," said the couple wanted to keep it a small family affair.

That prompted Kim Bum Soo to ask if he was invited. Ji Sung said that Kim was invited and would be asked to sing.

Lee Bo Young and Ji Sung met on the set of the drama "Save The Last Dance For Me." Her character character lost Ji Sung to his leading lady, played by Eugene. But in real life, they began to date.

They decided to marry this spring but postponed their announcement until Lee Bo Young finished filming her hit drama "I Hear Your Voice."