Monitor Problems Grey smudge!

Well this is unexpected.

Went outside, left computer on for about 40mins (was downloading some games)
Came back


Now my monitor has developed what I can only describe as a grey diffused semi-circular, pencil like smudge starting at the of screen edge, right on the lower part of the monitor (in the middle) extending 2 inches upwards.

Benq 2222HDL (I also updated amd drivers to 12.6 today an hour before this happened but I doubt its that?)

Need some help guys

Thanks

In all apps ? Checked cables ? Swapped in a spare monitor ?

yep all apps, other monitor is fine going to check cables now

just turned the monitor on now after a few hours and its still has the grey patch. :(