Wild Stallions 
[@Background Pony \#3CF8](/images/3132471#comment_10553546)
It is an interesting theory, I'm not too sold on the idea of Sunspot and Stellar Flare being siblings, but it makes for amusing reading. There is another fan theory that Sunburst and Starlight Glimmer are brother and sister, not one I followweither. Although, oddly enough, this comic series does imply that Sunspot and Firelight used to gang bang Stellar Flare during their college years. :P
It is an interesting theory, I'm not too sold on the idea of Sunspot and Stellar Flare being siblings, but it makes for amusing reading. There is another fan theory that Sunburst and Starlight Glimmer are brother and sister, not one I follow