Lack Of Filial Piety
Disobedience To Parents
noun, な adjective
You know that 不孝 means "disobedience to parents. So, if you add parents to it, it just means the same thing. Just a longer version of the word, basically. This means lack of filial piety or disobedience to parents.
The reading for 不孝 is the one you learned. Then, add 親's reading (vocab) to it.
もう手遅れですが、私は本当に親不孝な息子でしたよ。
It’s already too late, but I was a really disobedient son.