Question: Who is Apa Qaghan's paternal grandfather?
Sentence (from "Muqan Qaghan"): , personal name: 阿史那燕都, āshǐnà yàndōu, a-shih-na yen-to) was the second son of Bumin Qaghan and the third khagan of the Göktürks who expanded their khaganate and secured the borders against the Hephthalites.
Relevant evidence: Yes