Moreover, I will establish his kingdom for ever
The same is said in ( 2 Samuel 7:13 )
if he be constant to do my commandments, and my judgments, as at this
day;
if he continued in the observance of them, as he had begun, and went on in until that day; this is added here, and was not spoken by Nathan, when what goes before was; for Solomon was not then born, but must be suggested to David since, and as it should seem at this time.
The Brenton translation of the Septuagint is in the public domain.