I couldn't get the secret ending after doing all paths, but there seemed to be a simple solution! In case someone else has the same problem: In each run I generally avoided overly inappropriate comments/actions (like slapping people on the rear, telling the prince I was there to oogle) so I did a run where I did all this and had a more 'outrageous' personality. After that - the secret ending opened up. It may be that it wants you to try with both personality types.

Does anyone know how to get chosen by the King? Like what choices to make?

Not necessary to be as thorough as Love Sensei. Like Senrou said- you just have to make sure you do one play through all the way and go all the way to to the end on each person. I started from the beginning on each one and went all the way through to the end till I got back to the title screen. Thank you so much for the guide! It was a big help,

Well what I did was went through every route first (the way I wanted) I received every photo from everything else leaving only three photos for the secret route(btw save at the boat scene to get all images/reactions) and then I played one more route as if I wanted to listen to my mother the whole time I fainted from a bee for crying out loud! The king choose me and this time Gulli didn't love me. After that i STARTED from the beginning and got the secret option to pop up! XD

Nvm to my 1st comment after going through all the routes again clicking pretty much every option n going completely through them it unlocked...so basically the key is 100% thorough completion of each route for those of u still lost.

i have the same problem as @Remy has anyone figured out how to solve this???

Remy, I don't believe it's the first choice in the carriage ride. I think it's a few questions/choice menus into that scene, if I'm recalling correctly.
If you get to the end of the carriage scene and the option still doesn't come up, then I'm not sure.

First off, thank you for the guide.
Second, I romanced EVERYONE and yet I'm still not getting that secret romance. Planned to overthrow the government with Leopold, ran away with Bastien, journeyed to see kites with Charlotte, got fade out kisses with Sofia and Guillaume. But have yet to see the "Please don't ask me that" to activate. <_< I've got to be missing something.

Thank you! <3