Poor guy. 
At least he seemed to be pretty comfortable right to the end, though.
RIP Lost In The Fog.
Well, not always. At the barn I used to keep my horses, my trainer had 6 lesson horses and 4 of them were pure-bred QHs. They all did perfectly well in English events (predominantly jumping). They jumped at around 3ft easily and one of them is around 17hh and could jump a 5ft as if it were nothing. My friend also owns a QH who jumps and does dressage. Another one om my friends owns a Quarter Pony (QH X Welsh Pony) and gosh, that thing can jump! lol.
Poor Lost In The Fog. He was such a great horse. He will never be forgotten. Poor, poor boy. What a horse. A true champion.
Last time I checked, the QH registry hadn’t closed it’s stud book and so a horse with a TB parent could still be registered as a QH (granted, that was about 10 years ago). I never could figure out why you’d register it Appendix if it could be full. 
I had a feeling it was too good to be true. Poor boy. I hope he is dancing free in horsey heaven… and that there are lots and lots of carrots, apples, oats, and sugar cubes.
An Appendix QH gets Appendix papers when it’s registered with AQHA. To become a stud the horse has to earn enough points to earn it’s full QH papers. It makes an appendix “worth more” after they earn their QH papers. My last QH was actually mostly TB since his dam was a TB and his sire was an appendix but he earned his QH papers in his first year of showing. Kinda like an honor thing for an Appendix to earn his/her full papers. 
Ahh… so they all start off Appendix (the part-breds) and then earn their way into full QH status by showing? That makes a certain amount of sense.
Sorry about the delay of reply…
But, yeah that’s basically what happens and why we have 17.1 h lanky QH’s now in the hunter ring. But hey I love a horse that has the look of a TB but has the mind of a QH. Just a perfect combo i think.
My 28y/o Quarter Horse is actually about 1/4 thoroughbred. He’s tall, but very study and well built. His lines go four generations back to Three Bars (TB), and he’s got some random other TB blood mixed in. But, his lines are some of the best old-school foundation QH lines you can find (and especially in horses that are still with us today!). Mixing TB has been going on for ages in the QH world, and you can find Three Bars blood in a large percentage of QH’s today. And also, my horse has always been dominant in the open English Pleasure ring- someone said that you don’t see QH’s in English events… simply not true in some places especially in the Midwest and South. Especially when you look at the QH Congress and World Show- there are some CLASSY English horses there, even if they have some TB in their blood. I’ve also ridden QH’s that jump very, very well. I agree with what Holly said about QH and TB being a great combo- not that TB’s are firey or anything but in my opinion, the QH in them makes them very level-headed- a great, athletic horse for a wide variety of diciplines.