On what date was the album containing "Unforgettable" released?
Unforgettable (Thomas Rhett song):  It was released to country radio on July 28, 2017 via Valory Music Group as the second single from his third studio album, "Life Changes" (2017). Life Changes (Thomas Rhett album):  Released on September 8, 2017 through Valory Music Group, Rhett produced the album alongside Dann Huff, Jesse Frasure, Julian Bunetta and Joe London.
September 8, 2017