Complex sentence: Duet Mania was created in 1999, when the Bulgarian Music Producer Valentin Markov (PolySound) decided to put together a female pop duet and he was the one who gave the name of the duet.
Split into simpler sentences: Duet Mania was created in 1999, when the Bulgarian Music Producer Valio Markov (PolySound) decided to put together a female pop duet. He was the one who gave the name of the duet.