What tense is 見えなく?

[icewizard]

From this sentence 地下に入って、 富士山が見えなくなった 。

[Ncastaneda]

edit: or more like negative of 見える with naru attached in past tense
So it would be like," I entered the subway and Mount Fuji became unseeable"

[MissMisc]

To clarify, it’s the negative of 見える (見えない) + past of なる (なった), the い in 見えない gets conjugated like a regular i-adjective and changes to く

見えない く + なった → “… and it became that (Mt. Fuji) couldn’t be seen”

[Sezme]

Both replies above are accurate, but just to add further context, you can think of it as analogous to 食べたくなった which is 食べたい + なった or “started to want to eat”. In a negative form, it would be 食べたくなくなった which is 食べたくない + なった or “started to not want to eat”.