One guard was a veteran and the other was a new recruit and Celestia has the have sex with the veteran taking the submissive role. Haven't thought about it in years but now I can't seem to find it.

Why are you asking it in the M/M group is sound hetero to me

7693216
It might be The Princess' New Clop by cloppyhooves

7693244
Has them* referring to the two guards. Typo on my end

7693629
Unfortunately not.