Internal wall supporting gable end wall?

[Ouch77]

Above is a crayon'd plan of my house (1930's brick, gable roof) before extension work started. I'm kinda curious about the function of the wall highlighted red joining the chimney stack to the rear gable wall. All of the first floor walls, except this one, are fibreboard over timber. This is single skin brick. Downstairs the internal walls are similarly single skin brick. The chimney stack is brick (obviously) and downstairs is more massive to incorporate an integrated oven.

Anyhow, as part of the extension/renovation I'm wanting to demolish all that is marked in red, eventually. (the chimney stack is gone from top down to first floor ceilling)- I'm aware there'll be a need for supporting of the upstairs floor when the stack comes down to that level, but that's another issue. I'm confident that this upstairs rear internal wall is not directly supporting any ceiling/roofing elements.

So...

What could the purpose of the single internal brick wall be? Why did the designers decide to include it?
Is it supporting the chimney stack against the rear wall? or is it supporting the rear wall against the chimney? maybe a bit of both?
Will my house fall down if I remove this wall (the chimney stack will come down first/at the same time)??

thanks..

 

[^woody^]

If anything, the only thing internal walls support in houses are floors and roofs.

 

[Ouch77]

If anything, the only thing internal walls support in houses are floors and roofs.

Roof is raised tie design, with big purlins running front to back, and relatively thin (3") ceiling joists running across - the wall in question barely touches them.