Can anyone tell me why in the genealogy of Jesus in Mt. 1 mentions two sons of Judah?

1The book of the generation of Jesus Christ, the son of David, the son of Abraham. 2Abraham begat Isaac; and Isaac begat Jacob; and Jacob begat Judas and his brethren; 3And Judas begat Phares and Zara of Thamar.

We have been taught that the linage of Jesus went through Phares then what role does Zara play?