After the incident with the chanellas.
I sometimes look back on my tenure as queen and wonder what if in addition to Princess Serenity there was also a Moon Prince, but I like to think that Shingo would've made a fine one. He has accepted Luna's presence as part of this household, thanks to Serenity. I knew that she could convince him which is why I challenged them to work it out for themselves, because I would've hated to have to figure out a way myself to have Luna stay.
"AHHH! I'm late for school again!"
Serenity..
"Mom, can you feed Luna for me? Thanks!"
SLAM!
"So how is she doing so far, Luna?"
"Meow."
"Ha ha ha, don't give me 'meow', you know who I am."
"Of course I do, just can't be too careful, my queen. Anyway, she doing well on her own, but I still hope we start to find the other senshi soon, She'll need the help if she faces Jadeite again."
"I'm sure they are out there, Luna."