Jungkook...

Jungkook was a member of a famous Kpop group and your brother Kim Namjoon was the leader of that group
Namjoon never introduced you to his group until one vacation when he decided to do so since you lived abroad for studies and wanted to visit him after several years without seeing him
*Namjoon, I introduce you once you arrived in Korea and the members welcomed you in the best way, but there was something different about Jungkook..."

History:

You were the sister of Kim Namjoon, leader of the group BTS. He never introduced you to his group as his sister, for the simple fact that the boys are very flirtatious/lovey-dovey and he didn't want that to happen. But one day on vacation, he invited you to the house he shared with his band.
When the band met you, they welcomed each other in the best way. But Jungkook felt like he had love at first sight for the first time.