Kim was born Han Jae-joon (hanjaejun; Han Zai Jun ) in Gongju, Chungcheongnam-do, South Korea. His real birthday, as revealed by his biological mother, was on 4 February, instead of 26 January. At a young age, he was given up for adoption by his biological mother to the Kim family, and his name was changed to Kim Jae-joong. When Kim was fifteen, he moved to Seoul by himself in order to take part in the auditions held by SM Entertainment.

On 17 January 2013, Kim released his first solo EP titled I/MINE, a rock-themed album which Kim penned all the lyrics to. The album debuted at the top of both the Hanteo and Gaon weekly charts in Korea. It was also met with resounding success throughout Asia, topping Taiwan's Five Music's Korean and Japanese music chart, Japan's Shinseido weekly chart and Yin Yue Tai's V chart for K-pop. It also topped the iTunes rock charts in nine countries. Additionally, the pre-released single "One Kiss" and lead single "Mine" topped both domestic charts and foreign charts, including a German Asian music chart.  On 26 and 27 January, Kim held two days of special concerts at the KINTEX Ilsan to celebrate the launch of the album, as well as his birthday. Kim then released a repackaged version of his album, titled Y which consists of contains two additional tracks: "Only Love" and "Kiss B" . The album was met with success and sold 50,000 copies upon release.  His first full-length solo album, WWW was released on 29 October 2013. A single titled "Sunny Day" was released ahead of the album and topped the iTunes EP chart in Japan. A repackaged version of the album, WWW: Remove Makeup was subsequently released in January 2014 and included the title track "Heaven", a pop ballad with label-mate Gummy. To promote his first album, Kim embarked on his first Asia tour which traveled to regional countries like Japan, Taiwan and China.  His second solo album, No.X was released on 12 February 2016. It topped iTunes charts of 39 countries around the world upon its release, and was named the most popular K-pop album in China for 2016.

Using a quote from the above article, answer the following question: What was his best solo album release?
His second solo album, No.X