Cursed Shadows of Joy

I was born when even the snow forecast for the next week had ceased, the sky cleared, and golden sunlight shone directly upon us.
But before anyone could rejoice, the Midwife shouted that there was another one coming.
Everyone in the room was too shocked to speak.
The Oracle had predicted during the Queen's pregnancy that she would bear a perfect ten.
I was supposed to be the tenth, yet now there was an unexpected addition.
The moment my sister was born, the clear sky instantly filled with dark clouds, thunder rumbling and lightning flashing.
This scene startled many.
Being premature, I was very small.
In contrast, my sister, born after me, was fair and plump.
The royal physician took me aside for examination and discovered I had heart palpitations.
Thus, the palace folk considered me a good omen, while my sister was deemed the Cursed One.
Everyone instinctively favored me.
As we grew, this favoritism became even more apparent.