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.
When Yoo In Na attended IU's concert last year, IU pointed at Yoo In Na while singing her hit song 'The Shower'.
As the audience know of Yoo In Na's presence through IU's touching gesture, Yoo In Na started to burst into tears.
Then the actress waved back to IU and took multiple pictures of her as well.
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)