Never? (I guess you just don't speak for all Mormons or Mormon general authorities like you think you do)
I expect a humbling acknowledgement here that you are wrong, or were simply mistaken:
Elder Trevor Christensen, who was serving as a Mormon missionary in the Florida Tallahassee Mission. Here's what "Elder" Christensen blogged:
"There was one thing needed, a Savior, an ultimate and eternal sacrifice. Lucifer, or Satan, his name means "Son of the Morning" meaning that he was a very choice spirit of our Heavenly Father, offered himself to be the sacrifice so that all will be saved no matter what, but he wanted all the glory to be his, and not our Father's. Christ then offered himself as the sacrifice and said the glory should go to our Father. Christ is our elder brother, Lucifer is our elder brother, we all are sons and daughters of God, so therefore, Satan and Christ are brothers.
Where'd all the good people go? (Sept. 28, 2009)
Perhaps his brother, Lucifer, had heard him say when he was still but a lad of twelve: Wist ye not that I must be about my Fathers business? (Luke 2:49).
Ensign, December, 1980: Jesus of Nazareth
Never? (Shall I keep going?)
"You will recall that Lucifer, our elder brother, proposed that he should be sent to this earth as our savior."
Marie Fox Felt, The Instructor, May 1941
Never? (Shall I keep going?)
Here's a Mormon writing online who concludes "The LDS gospel is very different than any other that has ever known to exist. Philosophically speaking it is the only form of Christianity that makes any sense." (So you know he's a faithful Mormon).
In that same July 11, 2012 post, he (Water Dog) wrote:
4) Premortal - Christ our elder brother, Satan also our elder brother.
MormonDiscussions.com: For Water Dog: Wildly unique concepts in the Book of Mormon?