Yari Dulom won the Daporijo assembly seat by defeating lone Arunachal Congress rival Daklo Nidak.
"We always said Tuki did not have a majority. His resignation proves BJP right as well as the actions of the governor," its national secretary Shrikant Sharma said.
Thirty-eight Congress legislators have revolted against Chief Minister Mukut Mithi to form the United Democratic Front and elected Apang as their leader.
The Supreme Court on Thursday virtually paved the way for government formation in Arunachal Pradesh by vacating its order on maintenance of status quo.
The Supreme Court on Monday refused to pass an interim order on a fervent plea of the Congress against "illegal" swearing-in of its rebel leader Kalikho Pul-led government in Arunachal Pradesh.
'The Congress, all these decades, worked on a slow Hindi-isation and Indianisation of Arunachal tribes. The RSS wants rapid Hinduisation,' says Shekhar Gupta.