Complex sentence: In 2004, SME and Bertelsmann Music Group merged to become Sony BMG Music Entertainment, although later, in 2008, Sony acquired BMG's stake and the conglomerate reverted to the SME name.
Split into simpler sentences: In 2004, SME and Bertelsmann Music Group merged as Sony BMG Music Entertainment. When Sony acquired BMG's half of the conglomerate in 2008, Sony BMG reverted to the SME name.