If you had been born into an English-speaking family who lived in a non-English-speaking country, you'd still be considered to be a native speaker of English if that was your natural language.

It reminds me of musicians I've heard speaking of their 'natural' instrument, meaning the one on which they'd first learned to play--that is, if they'd learned primarily on one instument in the beginning of their work. When I studied violin late in life, I automatically *saw and *heard things pianistically, and it took a long while before I began to *see and *hear thing violinistically.