Lee Jong Suk wrote a letter to his fans to personally confirm his romance with IU after Dispatch made the big relationship reveal on New Year's Day. In his note, he mentioned the name "Kang Dan I," comparing the singer-songwriter to this character, so who is she, and what does she mean to their relationship?

Lee Jong Suk couldn't help but get sentimental while writing his letter to fans while talking about his romance with IU. After revealing that "there was always a part of his heart" belonged to the actress, he said she was like "Kang Dan I" to him.

Though it may be puzzling to some, K-drama fans know how to solve this mystery perfectly. They even find it a romantic confession from the 33-year-old actor.

Kang Dan I is the name of the lead woman character in the 2019 K-drama "Romance is a Bonus Book," played by Kee Na Young. She's a strong woman who can surpass life and work obstacles.

Sure, this description fits IU, but it's more than just the personal traits. The show's fans revealed, via Koreaboo, that Lee Jong Suk's character in the series, Cha Eun Ho, had a longtime crush on Kang Dan I.

Hence, many believe that just like Cha Eun Ho, he has been crushing hard and in love with IU for a long time, but the situation has kept them apart. Despite that, they still end up together, just like the characters in the series.

Meanwhile, Dispatch broke the news about IU and Lee Jong Suk dating on December 31, per Soompi. Allegedly, they have been dating for four months after meeting on "Inkigayo" a decade ago.

The two have been friends since then, but their friendship eventually becomes romantic. Dispatch even claimed they spent Christmas together in Nagoya, Japan, and enjoyed a three-day vacation at a luxury resort.

Allegedly, the "Big Mouth" star personally planned their getaway and flew IU and her younger brother out to Japan first. He even prepared a pick-up service for them at the airport and joined them later.

Later, IU and Lee Song Juk's respective agencies confirmed their relationship in separate statements. HighZium Studio claimed that the couple's romance developed from being close acquaintances to a romantic couple, and they're now in a serious relationship.

"Please show lots of support so they can continue their beautiful relationship," it said. Alternatively, EDAM Entertainment said the same thing and asked fans to warmly accept Lee Jong Suk and IU's new relationship.