Ahead of yesterday's 3-2 defeat at Emirates stadium, the Irishman told the Sunday Sun: "Arsene Wenger called me in and told me about the offers and he left the decision up to me. He said I could stay at Arsenal or, because there were so many strikers in front of me there, he said he would understand if I wanted to leave.
"To be honest, it wasn't a hard decision to make because, at the end of the day, I wanted to play first-team football.
"It didn't look like I was going to be playing first-team football at Arsenal for the foreseeable future so in that sense it was an easy decision.
"The fact that Roy Keane is the manager here is one of the main reasons I joined.
"In Ireland he is a legend and, for me as a youngster, he is also a great person to work with.
"It was very close between Sunderland and Charlton but once I had spoken to Roy Keane, I had more or less made my mind up.
"Charlton were in the Premier League at the time and Sunderland in the Championship, so obviously Premier League football was an attraction, but I spoke to the gaffer and it was pretty clear that he didn't intend to be in the Championship for long!
"I know I made the right decision to leave Arsenal."