Chelsea have signed Arsenal striker Olivier Giroud on an 18-month deal for about £18m.
France international Giroud, 31, leaves Arsenal having scored 105 goals in 253 games since joining Arsenal.
Earlier on the closing day of the winter transfer window, Dortmund sold Pierre-Emerick Aubameyang to Arsenal.
Giroud: "Chelsea is one of the biggest teams in the Premier League - they have won maybe the most trophies in the last six or seven years,"
"It's a massive club and I am proud to sign for Chelsea, and I'm looking forward to playing."
Giroud's final appearance for Arsenal was as a substitute in Tuesday's 3-1 defeat by Swansea.
After his move to Chelsea was confirmed, Giroud thanked Gunners fans for their part in a "beautiful story" after "five and a half amazing years within the Arsenal family".
"I would like to especially thank the fans for their unconditional support upon my arrival," he wrote on Twitter.