How many books of skull dugery pleasant is there going to be?

There are going to be 9 books 3 of them have been released these are

Skulduggery Pleasant

Skulduggery Pleasant playing with fire

Skulduggery Pleasant the facless ones

The next one is coming out on the 4th of April (in the UK) It's going to be called

Skulduggery Pleasant dark days

ROCK ON SKULDUGGERY PLEASANT