"We received an enormous offer that gave us no choice but to let our goalkeeper leave," said Genk director Dirk Degraen at a press conference.
"But I have mixed feelings about this transfer: Genk wanted Thibaut to stay a bit longer."
According to Belgian media, Chelsea have paid nine million euros ($12.7m) to acquire the goalkeeper, who has been compared to recently retired Dutchman Edwin van der Sar.
Courtois, who is a full Belgium international, was under contract with Genk until 2014.
"Chelsea see me as the successor to Petr Cech," the Belgian said recently.
"It won't happen in one or two years, but in three, four or five years. I can therefore work on my development in peace."
Source: AFP
Source: AFP