Joe Cole insists Kai Havertz has been a 'great signing' for Arsenal and wishes the former Chelsea star stayed at Stamford Bridge last summer.
The two London giants are set to lock horns at the Emirates on Tuesday, with Arsenal top of the Premier League after beating Wolves 2-0 at the weekend.
Chelsea, meanwhile, head into the London derby off the back of their bitter FA Cup exit, having narrowly lost 1-0 to Manchester City in Saturday's semi-final at Wembley.
Havertz, who has nine goals and five assists in the Premier League this campaign, will hope to keep pressure on title rivals Manchester City and Liverpool by inspiring the Gunners to victory against his former club on Tuesday.