North Korea has released a South Korean student who has been detained since April.

South Korea’s Unification Ministry said that the North freed Joo Won-moon, a New York University student, through the truce village of Panmunjeom around 5:30 p.m. on Monday.

The Seoul government plans to investigate details on how Joo entered the communist country.

The North’s Red Cross Society notified the South earlier in the day that it would hand over Joo to South Korea.

The 21-year-old student was arrested by North Korean authorities on April 22 for illegally entering the country by crossing the Yalu River from Dandong, China.

In an interview with CNN that aired in May, the South Korean citizen who holds permanent residency in the United States, said that he had hoped to positively affect inter-Korean relations by entering the North.

The Seoul government said that it is a relief that the North has decided to release Joo, but the North should also send home three other South Koreans, Kim Jung-wook, Kim Kuk-gi and Choe Chun-gil, who are still held in the country.