Don’t know why I ship these two so much, guess I just like the idea of the snobby noble falling for a soldier, and of course I had to make it gay 

Alright, headcanon time:So I believe all nobles and royals have personal guards assigned to them, more often than not as just a formality and to make ponies feel safe.  Now Blueblood, being to snobby and insufferable noble he is, has gone through many personal guards, either Blueblood dismissing them himself or the guards requesting a transfer.  Now, during a trip to the Crystal Empire, Blueblood was assigned a new guard, Flash Sentry.  Now, unlike previous, Flash is much more laid back and awkward than the average soldier, so his interactions with Blueblood are very different from what the noble was used.  Flash would try to have small talk with Blueblood and try to joke around with him, basically treating the proud noble as if he was any other pony.  At first, Blueblood hated it, “How dare this peasent speak to me as if we are equals” but slowly he started to look forward to their conversations.  For the first time, Blueblood encountered a pony who didn’t care about his title, heritage or wealth, all Flash cared about was who Blueblood was as a pony. 

Eventually Blueblood returns to Canterlot, and Flash joins him, officially becoming his permanent royal guard.  Their close friendship slowly becomes romantic, with Blueblood in denial and Flash more than happy to just be with the noble, teasing him every now and then.  At last Blueblood accepts how he feels and the two start a beautiful romance, eventually having a spunky little filly.Sure there were quite a few nobles who were disgusted by Blueblood’s choice, mainly because his partner was of a lower class rather than it being a gay relationship, though a few were unhappy about that too.  But with Celestia and Luna’s blessing, the two were able to wed and live far happier lives.Hooray for happy endings