Romelu Lukaku has signed a five-year £28m deal to join Everton.
The 21-year-old Belgium striker was a £18m signing for the Blues from Anderlecht in 2011 and the hefty £10m profit will grow to £13m with add-ons agreed between the two clubs.
Lukaku never impressed in his 15 outings for the Blues and the remarkable transfer fee is due in part to his young age and what he has done on his loan spells at WBA and last season at Everton.
Chelsea have three senior strikers to call on this season; Fernando Torres, Diego Costa and the returned Didier Drogba.
Mourinho again said the transfer window is closed but he said that before netting Drogba too.
But technically Drogba was not a transfer as he was a free agent, so the PR spin goes. So a fourth addition to the striking role is a possibility if the player is a free agent, as is as likely, Chelsea promote one of the kids from the under-21s to warm the bench for the season.