What was the relationship between Nathan and Jesus?
Nathan brought David the promise of a kingdom forever. The angel Gabriel told Mary that Jesus would reign forever on the throne of David. 2 Samuel 7:16-17; Luke 1:32-33
What the Bible says
2 Samuel 7:16
And thy house shall be faithful, and thy kingdom for ever before thy face, and thy throne shall be firm for ever.
Luke 1:33
And of his kingdom there shall be no end.
Douay-Rheims Bible (Challoner revision), public domain.