Lukaku was was wanted back at Stamford Bridge over the summer as Chelsea striker Diego Costa flirted with a move back to Atletico Madrid.
But the Belgium international remained at Goodison Park and has enjoyed a stunning season so far, topping the scoring charts with 22 goals to his name already.
Antonio Conte tried to break Chelsea transfer record to re-sign Romelu Lukaku
But that fee was not enough for Toffees manager Ronald Koeman, who sees Lukaku as a central part of his project at Everton.
The Premier League leaders sold the 23-year-old for just £28m in 2014 after an initial loan spell and he's gone on to bag 83 goals in 157 appearances.
Romelu Lukaku has 22 goals for Everton this season
How Chelsea could look with Romelu Lukaku
Tue, March 14, 2017
How could Antonio Conte's Chelsea side look if they signed Everton ace Romelu Lukaku?
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How could Chelsea look if they signed Romelu Lukaku?
The powerful Belgian recently turned down the chance to become Everton's highest ever paid player in an attempt to find Champions League football elsewhere.
Lukaku said earlier this month: "You need the platform to show yourself. Then you are talking about Champions League and whatever types of games."