I vaguely remember that atleast once a new/returning character was announced but was axed before filming scenes.

Whenever a new character arrives and is hated, people quickly demand that they be axed. I don't usually agree with this since characters can improve with better storylines, however there have been one or two new characters who serve no purpose and are played by very bad actors.

I've always assumed that they won't be axed quickly since the character is new, but what's been the fastest axing of an actor/actress (who was hinted/announced as permanent not recurring) which has resulted in only a short stint onscreen? Perhaps it could be due to offscreen behaviour or to the producer realising that the character wasn't working out (i.e. not the actor's initial choice to leave).

Usually the cast have six months contracts to start with, this is then extended to a year if the actor proves his worth.

Wasn't the actor who played Danny Mitchell in EE axed in Kirkwood's cast cull of 2010? He was one of Santer's last character introductions.

Emmerdale Thomas King. Son of Carl. Lasted one month and was very suddenly 'needed back in Saudi'.
Not that it has anything to do with it of course, but it's not a good idea to leak advance storylines on Twitter.

Chris Fountain disappeared within weeks after being axed from Corrie.

Atleast 3 more months of Shakil then...

Oh god. Surely not 3 more months of watching him munch Rebecca Fowler's face off

Shakil needs to go

Sorry, that was wrong. The character wasn't axed, he's still in Saudi with his mother and could return recast.

There was the return of Trudy in Hollyoaks that never came to pass because of an issue with Westbrook (everyone gave a different story). This led to Kierston Waering joining the cast very briefly

In Prisoner, the Barnhurst Five got the boot 7 months after they appeared.

Prisoner was apparently shot six months ahead of transmission. So this could mean that they were got rid of a month after their first episodes were aired.