Title: Lille and Chelsea Reach Agreement to Sell Midfielder for 35 Million Euros

Chelsea, the Italian powerhouse, has signed a deal with Lille, one of Europe's top clubs, in which they have agreed to sell their most valuable player in the club's history, Diego Costa.

The transfer is expected to be completed by the end of this month, and it will cost the Blues a reported 35 million euros ($44.2 million) per season, according to reports from the French newspaper Le Parisien.

Costa, who joined Chelsea from Real Madrid in 2017, has been a key figure in the club's success since his arrival. He has scored more than 200 goals for the club, making him one of the best players in European football.

The Blues were reportedly keen on signing Costa but ultimately decided against doing so due to financial constraints. However, Chelsea now have the option to sign Costa for a lower price or even sell him for more money if they feel that he can still contribute to their team.

The move comes just months after Chelsea announced plans to strengthen their defense, with the club reportedly looking at buying a new goalkeeper and adding another centre-back to its squad.

Chelsea's decision to sell Costa was seen as a smart move by the club, given their financial situation. They had already invested heavily in the club's youth academy and training facilities, while also investing in the recruitment of young talent.

It remains to be seen whether Chelsea will be able to attract a replacement for Costa, but it seems likely that they will try to make a strong offer for him. The transfer fee could potentially be as high as 60 million euros ($70.2 million), depending on the negotiations between Chelsea and Lille.

In conclusion, Chelsea's decision to sell Diego Costa is a significant development in the club's history. It will help the Blues to strengthen their defense and improve their chances of winning titles in the future. While there may not be a suitable replacement for Costa, the club will certainly look forward to the potential offers that could come their way in the future.