The 12-year-old was linked with French sides Lyon and Bordeaux, but has decided to move to London.
Boga’s father has been living in London for two years, something that made the move possible.
“That is not a transfer, as the rules forbid it,” Hillion told Les Dessous du Sport. “We couldn’t have signed Jeremy if Mr Boga hadn’t been in London.
“Chelsea took him because he has the talent to play at the highest level. He’s an excellent number 10.”
ASPTT Marseille was disappointed with the move and an director declared: “We have had no news from the Boga family neither from Chelsea, this happened behind our back.”