The deal was with a view to a permanent transfer, which has now been finalised with the forward signing a three-year deal.
Fagan was a trainee at hometown club Birmingham City, and played 9 minutes of Premiership football in 2002 before loan spells at Bristol City and Colchester. The latter was made into a free transfer in March 2004, but just under a year later he left to begin his first spell with Hull City. The transfer fee was officially undisclosed, but was reported to be worth around £125,000.
He helped City to promotion from League One in the remaining months of the 2004/05 season and then impressed in the Championship. However, with his contract coming to an end, City decided to sell in January 2007. Derby paid £750,000 up front, with an undisclosed payment to be paid after they achieved promotion four months later.
The 25-year-old made 22 appearances for the Rams in the Premier League, and was on the losing side in 16 of those games. He did not play in their solitary win of 2007/08.