Complex sentence: In March 2012, he was listed by "Forbes" magazine as one of the richest Russians with an estimated fortune of $1.1 billion, however his fortune has since declined, and he is no longer considered to be a billionaire.
Split into simpler sentences: In March 2012, he was listed by "Forbes" magazine as one of the richest Russians with an estimated fortune of $1.1 billion. However, his fortune has since declined, and he is no longer considered to be a billionaire.