Genesis 36:12
And Timna was concubine to Eliphaz Esau’s son; and she bare to Eliphaz Amalek: these were the sons of Adah Esau’s wife. And Timna was concubine to Eliphaz Esau’s son; and she bare to Eliphaz Amalek: these were the sons of Adah Esau’s wife.
Amalek is the grandson of Esau, the son born to Eliphaz, Esau's son, through Timna, Eliphaz's concubine. The verse belongs to the account of Esau and the nations that sprang from him, set at the time when Jacob was about 109 years old, Joseph was 17, and Benjamin was a small child two to four years old. The Amalek named in the verse was among the descendants of Esau whose families became part of Edom.
The verse presents Amalek as the ancestor of the Amalekite tribe, who gathered other kin around them and became a strong and warlike nation and the first to attack Israel. This ancestry explains why Amalek is described as sharing Esau's old hatred of Jacob's descendants and seeking to destroy them. The union of Eliphaz and Timna is described as adulterous, and the Amalekites are said to have inherited fierce hatred against God.
The Amalekites remembered the prophecies concerning Jacob and Esau and Jacob's taking of the birthright and blessing. Since God had forgiven Jacob's sin and Esau had forgiven Jacob, the Amalekites as kinsmen ought to have helped their brethren Israel instead of making war on them. Because of their greater sin and cruelty to their kinsmen, God pronounced utter annihilation upon them. As Jacob was saved from Esau through prevailing prayer, so Jacob's descendants were saved from Esau's descendants as a token of God's faithfulness to his promises. Yet the name alone does not prove that the Amalekites descended from Esau, since the Amalekites were already recorded as a people before Esau's grandson was born, so their origin is unknown.