Flash Sentry was promoted from guard of the Crystal Empire to guard of Canterlot after Twilight became the princess of Equestria, and she made him her captain of the guard, entrusting him with protecting her and her family. Here he is walking with her and her son through the castle halls, escorting them out of the castle to the Crystal Empire, where he and his guards fly them to on their royal chariot.

Notes: This takes place in an alternate universe where Discord didn't turn out to be Grogar and the mane 6 are married with children. Also Gallus has a different future job then captain of the guard in this verse, likely a teacher at the school of friendship. The middle glass stained was edited to add Grogar to it and this is Twilight's future appearance in my universe which I find better than her having Celestia's design.