Complex sentence: In 2011, Tisci was widely considered to be John Galliano's most likely successor as head designer of Christian Dior; however, in 2012 Raf Simons was announced as Galliano's replacement as creative director.
Split into simpler sentences: In 2011, he has been widely considered to be John Galliano's most likely successor as head designer of Christian Dior. However, in 2012 Raf Simons was announced as Galliano's replacement as creative director.