Your horse has a wonderful pedgree for dressage, at least the part you have described.
St. Moritz was a 2003 premium Hanoverian stallion by Sandro Hit out of a mare by De Niro. I don’t remember the details, but St. Moritz was euthanized a few years ago after suffering a severe injury.
Sandro Hit has been one of the most successful dressage sires of modern times. Although he did not compete past the Y/H classes, he has been very, very popular with breeders because he almost always produces leggy, elegant, big-trotting offspring (and always with dark coats - no chestnut foals). He has so many stallion sons I have lost count, as well as dozens upon dozens of State Premium and Verband Premium daughters, and his offspring are now starting to prove himself as upper level mounts (there are 3 Sandro Hit offspring going to the London Olympics as Team mounts).
De Niro is one of the top dressage sires in Germany. He is by the legendary Grand Prix dressage stallion Donnerhall, and De Niro himself also competed to Grand Prix dressage at quite a young age. He has proven himself as a formidable sire, producing numerous licensed stallions, premium mares, and top international quality offspring. He had EIGHT offspring on the official dressage nomination list for the London Olympics (tied with Jazz for the most offspring on the list), and of those 8 offspring, 2 were officially named to Teams, 2 were named as official Individual entries, and 2 were named as official Reserve entries.
Prince Thatch was a very good TB sire for the Hanoverians, passing in particular an excellent walk. His daughters have found great favor as broodmares - two of North America’s well known dressage stallions (Don Principe and Royal Prince) are out of Prince Thatch mares.