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?

Documents:
source: Gu Family Book
text: Gu Family Book 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.

source: Lee Seung-gi
text: Lee Seung-gi 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.

source: Lee Yu-bi
text: Lee Yu-bi Lee Yu-bi (; born November 22, 1990) is a South Korean actress. She began her career in the 2011 sitcom "Vampire Idol", then played supporting roles in television dramas "The Innocent Man" (2012), "Gu Family Book" (2013), and "Pinocchio" (2014), as well as the films "The Royal Tailor" (2014) and "Twenty" (2015). Lee plays her first leading role in "Scholar Who Walks the Night", adapted from the webtoon about a Joseon vampire scholar and a cross-dressing bookseller.

source: Cho Kyuhyun
text: Cho Kyuhyun Cho Kyu-hyun (born February 3, 1988), better known mononymously as Kyuhyun, is a South Korean singer and musical theatre actor. He is best known as a member of South Korean boy group Super Junior, its sub-groups Super Junior-K.R.Y., Super Junior-M and a former member of the South Korean ballad group S.M. the Ballad. He is one of the first four Korean artists to appear on Chinese postage stamps.

source: Choi Jin-hyuk
text: Choi Jin-hyuk Choi Jin-hyuk (Hangul: 최진혁 , born Kim Tae-ho on February 9, 1986) is a South Korean actor. He is best known for his roles in the television series "Gu Family Book", "The Heirs" and "Emergency Couple".

source: Refilwe Modiselle
text: Refilwe Modiselle Refilwe Modiselle is a South African model and entertainer born in Rockville, Soweto, and the country's first professional fashion model with albinism. She started her modelling career at the age of 13 when she was approached by "Y!" magazine. She also appeared as a runway model in 2005 for South African designer David Tlale, making her the first albinistic model to appear on a runway in South Africa.

source: Jo Jae-yoon
text: Jo Jae-yoon Jo Jae-yoon (born September 15, 1974) is a South Korean actor. He made his acting debut in 2003 and has since starred as a supporting actor in numerous films and television series, including "The Man from Nowhere" (2010), "The Chaser" (2012), "Gu Family Book" (2013), and "The Suspect" (2013). Jo also appears in the variety-reality show "Animals" (2015).

source: Stefan Pejic
text: Stefan Pejic Stefan Pejic (born 5 June 1988) is a Welsh actor, comedian, singer,entertainer born in Neath and raised in Swansea, Wales. He is a former Butlins Redcoat.

source: Yoo Yeon-seok
text: Yoo Yeon-seok Yoo Yeon-seok (born Ahn Yeon-seok on April 11, 1984) is a South Korean actor. After making his acting debut in 2003 with a small role in "Oldboy", he resumed his acting career in 2008. His notable works include the films "Re-encounter" (2011), "Architecture 101" (2012), "A Werewolf Boy" (2012) and "Whistle Blower" (2014), "Perfect Proposal" (2015), "Mood of the Day" (2016) as well as the television series "Gu Family Book" (2013), "Reply 1994" (2013), "Warm and Cozy" (2015) and "Romantic Doctor, Teacher Kim" (2016).

source: Kim Ki-bang
text: Kim Ki-bang Kim Ki-bang (born May 31, 1981) is a South Korean actor. Since his acting debut in 2005, Kim has played supporting roles in television dramas such as "Boys Over Flowers" (2009), "Golden Time" (2012), "Gu Family Book" (2013), "Medical Top Team" (2013), "My Lovely Girl" (2014), and "Heart to Heart" (2015). He played his first leading role in the film "Geochang Massacre - Bloody Winter" (2013).

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Answer: January 13, 1987