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他当爷爷了。
He has become a grandfather.
To become a grandfather; to have a grandson or granddaughter.
我爸爸当爷爷了,他很开心。
My father has become a grandfather, and he's very happy.
This phrase is commonly used to describe the moment someone becomes a grandfather.
In Chinese, family roles are often specified with phrases like 当爷爷 (grandfather), 当奶奶 (grandmother), 当外公 (maternal grandfather), and 当外婆 (maternal grandmother).
Derived from the verb 当 (dāng, to become) and the noun 爷爷 (yéye, grandfather).
This phrase is often used in family contexts to celebrate the birth of a grandson or granddaughter.