In what year did Hong Kong become a part of China once again?

After the First Opium War (1839–42), Hong Kong became a British colony with the perpetual cession of Hong Kong Island, followed by Kowloon Peninsula in 1860 and a 99-year lease of the New Territories in 1898. After it was occupied by Japan during the Second World War (1941–45), the British resumed control until 30 June 1997. As a result of the negotiations between China and Britain, Hong Kong was transferred to the People's Republic of China under the 1984 Sino-British Joint Declaration. The territory became China's first "special administrative region" with a high degree of autonomy on 1 July 1997 under the principle of "one country, two systems".