The sky was - well, I can't say replaced, because on my original jpg it was only white. So: the sky was placed by LuminarAI. I tried to find one that hits the mood. This is unfortunately more difficult than you may think, because spectacular skies are the main offers you get. I couldn't find just a normal cloudy sky, without any breathtaking light bursts ...
But as you can see, the whole thing is edited and manipulated - so take it, or leave it.
;-)