Midfielder Scott Parker joined Roman Abramovich's Chelsea on Friday in a 10-million-pound ($18.11 million) move across London from Charlton Athletic.
Charlton initially rejected a 7.5 million pound offer for the 23-year-old, who began his career at the South London club, with manager Alan Curbishley bitterly opposed to the deal.
"It's a team that is going places and it's something I want to be part of," Parker told a news conference.
"I can understand the Charlton fans but I've been there for 12 years and since I broke into the team four years ago all I've done is give 100 percent and never really let them down.
"I hope they understand my situation... This was an occasion I couldn't refuse.
"Charlton have been excellent to me and the fans have been brilliant...and so has Alan Curbishley. He's given me the chance and I really appreciate that."
Chelsea are third in the Premier League, six points behind leaders Arsenal, while Charlton are having their best-ever season in the top flight, in fourth and nine points further back.
Curbishley said he was forced to let Parker go due to his disruptive behaviour in training.
"There are lots of players who will kiss the badge of your club one week and then kiss the badge of another club the next," he told The Sun newspaper.
"Scott made it abundantly clear in more ways than 10 he didn't want to play for us any more.
"I'm not happy with the way the deal has been conducted."
Parker made his international debut as a second-half substitute in England's last friendly against Denmark in November.
Parker is Chelsea's only signing during the January transfer window and takes their spending on players since Russian tycoon Abramovich took over last July to 121 million pounds.
As part of the deal Chelsea's Carlton Cole, who has been at Charlton on loan since the start of this season, will remain there until the end of next season.