After revealing their relationship on New Year's Eve, IU and Lee Jong Suk wrote heartfelt letters to fans, posted on their official fan cafes.

Lee Jong Suk apologized as he surprised them with dating news and expressed gratitude to those who supported him.

“Hello. This is Lee Jong Suk. I wasn’t able to share a separate thank you message to fans after receiving a big award, so I am belatedly sharing this letter," he wrote.

"I am writing here for the first time in a while. I’m so sorry for surprising you at the end of the year. Thank you to the fans who yelled and cheered for me at the Drama Awards so I don’t lose my confidence,” the actor added.

After thanking fans, Jong-Suk shared how he met his girlfriend, IU, saying they already had feelings for a long time and remained good friends.

“We first met when I was around my mid-20s, and it was big beyond puppy love, but I had regrets as it couldn’t be achieved. We were friends for a long time, and now it turned out like this,” he said.

He sweetly described IU as 'she was like Kang Dan-i' to him and expressed how amazing she was.

“Even when I was working hard living my own way, she was a strange existence who always took up a corner of my heart. I think my fans will understand if I say that she was like Kang Dan I (character in “Romance is a Bonus Book”) to me,” Lee Jong Suk shared.

“She is an amazing person who helps me with my path and concerns of life as a friend, is someone I can rely on, is younger but sometimes feels older, and is like a grown adult but also someone I want to protect,” he added.

He also said that his girlfriend makes him want to be a better person and despite worries, he still asked his fans for love and support.

“I was so so thankful for the love and support you sent during this year where so much happened, and I was so glad we got to meet again. Happy New Year, and I love you always," he ended.

Meanwhile, IU also posted her letter, greeting fans with a happy new year as well as confirming her happy relationship with the actor.

She sent apologies to UAENAs, her fandom.

"Hello UAENA! Are you all asleep at this time? Wondering where you spent the end of 2022 and if you might have had a bit of confusing last day of the year because of me, today I came to relay new year’s greetings along with my gratitude and apologetic feelings,” the idol wrote.

She penned to fans an assurance that she is now happy having someone to rely on.

“He was a colleague for a long time, and we are building up positive feelings while relying on each other. He is a reliable and cute person who has supported me for a long time, always told me I’m amazing, and sent me sincere encouragement,” she added.

Since her fans were caring and supportive of her, IU, whose real name is Lee Ji-Eun, was worried about how they felt about the unexpected news.

“As UAENA always watches over me most closely, I think you must feel that I am in a time where I am emotionally comfortable and doing well. Along with that, I think one of the reasons that my pride and passion for work is surging even more these days is because I have a good friend who compliments me for a long time up close,” she wrote.

She then promised to ‘date quietly and beautifully’ to avoid fans from worrying and expressed gratitude for last year.

“Happy New Year everyone. In 2022, which has become last year, I was so happy to meet you for the first time in a while and see you up close. I will never forget those overwhelmingly happy moments.”

She ended with a sweet note, “Happy New Year again, UAENA. When you wake up from your deep sleep, it will be a new year. Sleep well. I love you.”