Complex sentence: The earliest use of tanaíste ríg' was in reference to an Anglo-Saxon prince c.628, and many subsequent ones related to non-Irish rulers, before the term was attached to Irish kings-in-waiting.
Split into simpler sentences: The earliest use of "tanaíste ríg" was in reference to an Anglo-Saxon prince in about 628. Many subsequent uses related to non-Irish rulers, before the term was attached to Irish kings-in-waiting.