Recently, an adorable photo set of good friends NS Yoon Ji and Yoon Seung Ah was revealed via NS Yoon Ji's twitter. In one photo, the girls are seen displaying a 'bad girl' energy with their haughty looks. Meanwhile in the other photo, they're shown smiling brightly, giving off a lovely appearance. The two have been nicknamed as the 'Yoon Sisters' because of their similar wavy hairstyles and baby-faced looks. The two became close friends when they received acting lessons together back in 2009. Because NS Yoon Ji had left her family in America and was living alone in Korea, Yoon Seung Ah took care of her like she was her real sister. NS Yoon Ji and Yoon Seung Ah have each debuted in their respective fields of singing and acting, but are still treasuring their never-changing friendship. They have become known as 'representative best friends' in the entertainment world. Yoon Seung Ah has been quite busy in the acting field with the MBC daily sitcom "All My Love" and NS Yoon Ji is preparing to release her new single on July 29th. Source + Photo: OSEN via Nate