Complex sentence: The band went on a hiatus in October 2009 to focus on side projects, and reunited in September 2011, releasing their fourth album, "Four" in 2012 which entered the UK Albums Chart at number three.
Split into simpler sentences: The band went on a hiatus in October 2009 to focus on side projects. They reunited in September 2011, and shortly thereafter released their fourth album, "Four", which entered the UK Albums Chart at number three.