Happy Ending (EP)

Members Heehyun and Chaeyeon joined the survival show Produce 101 in 2015 and due to this, they had to temporarily withdraw from the group.[1] Meanwhile, MBK Entertainment added a new member to the group, Eunchae, on March 7, 2016.[2] The company then announced that Heehyun and Chaeyeon will be joining the group for an upcoming comeback in June. The group filmed their new music video in Jeju Island and will be returning without Seunghee, who left to pursue an acting career after her contract expired on April 30.[3][4] Since April, Chaeyeon has been promoting with I.O.I after ranking 7th on Produce 101 and debuting in the group. I.O.I's promotions for their debut album ended on June 4, allowing Chaeyeon to return to DIA while I.O.I promotes in sub-units before she returns to promote with the group until their 1-year contract with YMC Entertainment ends.[5]

The group appeared with its new lineup for the first time on a Naver V-app broadcast held on June 7.[6]

Happy Ending debuted and peaked at number 7 on the Gaon Album Chart, on the chart issue dated June 12–18, 2016, achieving a new peak for the group, as their debut album peaked at number 11.[8] The EP also debuted at number 24 on the chart for the month of June 2016, with 4,820 physical copies sold.[9] The EP sold 9,474 physical copies in 2016.[10]