SEE ALSO: Sweet Sorrow's Sung Jin Hwan and Oh Ji Eun to tie the knot

Kim Young Woo shared the good news at his group's concert, '2013 Sweet Sorrow Christmas Concert' held at COEX, Samseongdong, Seoul on the 23rd-24th.

Kim Young Woo tweeted, "Also, joyful news on the birthday of Jesus Christ! Thankfully, I will become a father!!!!! ^^ I already told those who came out to the concert. My 'son' is '21 weeks' old right now!! ^^ hehehehe whatever the case Merry Christmas!"

Kim Young Woo tied the knot with his girlfriend Ms. Kim back in 2011 after six years of dating and will soon welcome their first child together!