The news broke after a source close to Jang revealed that the couple had long been an item and met up on a regular basis. They recently went on a trip together to Guam, the largest resort island in Micronesia, according to the source.
To back up the claims, the news outlet unveiled photos seemingly taken on holiday that Jang and Yuko separately posted on their respective Instagram accounts.
According to the reports, the alleged couple has been dating since 2006, and K-pop insiders already knew about the cross-border romance. Jang mostly stays in China and Korea for work, while Yuko travels between Korea and Japan to see her lover.
The two have yet to confirm the reports.
Jang, 35, debuted in 1996 as a member of first-generation idol group H.O.T. After the popular quintet disbanded in 2001, Jang returned to the stage with two fellow members Tony An and Lee Jae-won as a trio JTL.
Yuko, a year younger than Jang, rose to fame in the early 2000s by making appearances on Korean hit variety shows and dramas.
If the news turns out to be true, Jang would be the latest addition to a handful of Korean celebrities who recently went public about their relationships with international partners.
South Korean film director Kim Tae-yong and popular Chinese actress Tang Wei announced their wedding plans last week. Actress Chae Rim also confirmed her engagement to Chinese actor Gao Ziqi in June and another actress, Bae Doo-na, confirmed that she had been dating British actor Jim Sturgess for two years in May.
By Ock Hyun-ju (firstname.lastname@example.org)