Recently, the two stars' close friendship has become a hot topic online.
It is because IU mentioned and thanked Yoo In Na during her award acceptance speech at the '2017 Melon Music Awards' on December 2.
After awarding 'Best Album of the Year', IU said, "Though we are not blood-related family, I want to express my thanks to my best friend, my No.1 fan, and my muse, Yoo In Na."
Despite their age difference, IU and Yoo In Na showed their close friendship on various events.
It was reported that the two stars make sure to hang out together at least once a week despite their busy schedules.
(Credit= Online Community)