In a comment made on a previous question I asked, someone directed me to Moses 1:35 in the Pearl of Great Price. I read the context and saw Moses 1:32-33, which interested me as well. The text is as follows:
And by the word of my power, have I created them, which is mine Only Begotten Son, who is full of grace and truth.
And worlds without number have I created; and I also created them for mine own purpose; and by the Son I created them, which is mine Only Begotten.
In LDS teaching, Lucifer and Jesus are spiritual brothers, and, indeed, we are all brothers of both Jesus and Lucifer--both of whom are our elder brothers.
So, in what sense, then, is Jesus the Only Begotten Son of God according to LDS teaching, when in the pre-mortal life Elohim did have multiple sons (and daughters).