SBS' drama "The Legend of the Blue Sea" aired its fourth episode Thursday, maintaining its spot as the most watched drama for its time slot. Moreover, after Cha Tae Hyun's cameo, rumors are rife that Jun Ji Hyun's co-star in "My Love from the Star" Kim Soo Hyun will join for cameo appearance.

According to market research firm Nielsen Korea on Thursday, the drama drew viewership ratings of 15.7 percent. At second place was the KBS2 show "Oh My Geum Bi," with 6.5 percent, followed by MBC's "Weightlifting Fairy Kim Bok-Joo" with 5.7 percent.

Moreover, according to Hancinema report, "The Legend of the Blue Sea" beat this year's most popular drama's ratings of "Descendants of the Sun" with 2.1% increase of viewership ratings. With its continuous high ratings, viewers anticipate it to be this year's greatest production for the last half of the year.

Meanwhile, the drama viewers have already seen Jun Ji Hyun reunited with her "My Sassy Girl" co-star Cha Tae Hyun in the latest episode. On the November 24 airing of the SBS drama, Cha Tae Hyun made a special cameo appearance as a con-artist who tries to pull one over on Jun Ji Hyun, a clueless mermaid who is trying to adjust to life above water.

With this, fans are quick to speculate that soon "My Love from the Star" actor Kim Soo Hyun might appear in the drama.

Some speculated that this might be true as some of the actors and actresses are from Jun Ji Hyun and Lee Min Ho's drama. Like for example, Kim Seong Ryeong and Lee Min Ho were mother and son in the drama "The Heirs." Kim Seong Ryeong is playing the role of a chairwoman of Myeongdong Capital Jang Jin-ok.

Moreover, Lee Min Ho's mother in the "The Legend of the Blue Sea" drama, portrayed by Na Young Hee, is Jun Ji Hyun's mother in "My Love from the Star."

However, there were no official statements from SBS about the possible cameo of Kim Soo Hyun. "The Legend of the Blue Sea" airs every Wednesday and Thursday 22:00 (KST).