Christopher Nkunuku became Mauricio Pochettino's first signing as Chelsea manager when the France forward left RB Leipzing for the Premier League club.
The 25-year-old joins the Blues for £52m after scoring 16 times in the Bundesliga in 2022/23.
The previous season he scored 20 goals and contributed 15 assists in the league. That was when he became a target for top European clubs including Chelsea.
They are expected to have a summer clear out, with forwards Romelu Lukaku and Pierre-Emerick Aubameyang moving on, so Nkunku should add some much needed firepower to attack that looked blunt last season.
Chelsea will be aiming to improve on their disappointing 12th place finish.
They open their campaign at home to Liverpool on 12 August and are 2.588/5 on the Betfair Exchange to achieve a top four finish in their first season under Pochettino.