21:72 (Nafilah - Was Yaqoob AS grandson or son of Ibrahim AS?)

[Student]

Salaam,

Just caught my attention in my latest Quran reading, 21:72 mentions Yaqoob AS as extra (Nafilah) on top of Ishaaq AS - does that mean he was his son? Just curious now 

Any thoughts if I miss something explicit in the Quran that makes him the grandson of Ibrahim AS?