Question: When was the South Korean singer, actor, host and entertainer born who was known as Ballad Prince and was also a star of Gu Family Book?
Related documents: [0]  [DOC] Gu Family Book (; also known as Kang Chi, the Beginning) is a 2013 South Korean television series starring Lee Seung-gi and Bae Suzy. The fusion martial arts action historical drama is about a half man-half monster who is searching for a centuries-old book that according to gumiho legend, contains the secret to becoming human. [END] 
[1]  [DOC] Lee Seung-gi (Hangul: 이승기 ; Hanja: 李昇基 ; born January 13, 1987) is a South Korean singer, actor, host and entertainer. Known as the "Ballad Prince", Lee has had numerous hit songs such as "Because You're My Woman", "Will You Marry Me", and "Return". He has garnered further recognition as an actor with leading roles in popular dramas such as "Brilliant Legacy" (2009), "My Girlfriend Is a Nine-Tailed Fox" (2010), and "Gu Family Book" (2013). He was a member of the first season of weekend variety show "1 Night 2 Days" from November 2007 to February 2012, and the host of talk show "Strong Heart" from October 2009 to April 2012. [END] 
Answer: 
January 13, 1987
January 13, 1987