The Republic of Ireland winger put pen to paper on a five-year deal at Stamford Bridge after spending the weekend considering the move.
"This was probably the biggest decision of my life and I didn't want to rush it," he said.
"It was just a matter of thinking everything through. I had seven great years at Blackburn and there was no big reason to move but in the end I decided a big new challenge was necessary."
"This was probably the biggest decision of my life and I didn't want to rush it," he said.
"It was just a matter of thinking everything through. I had seven great years at Blackburn and there was no big reason to move but in the end I decided a big new challenge was necessary."