Flashback to a couple months earlier

Something happen one day.

during the summer.

The Park(the people who turned Jisung into a teen boy) were back.

Nct founded out that Chenle got blasted with that thing which caused him to age into a teenager.

That thing was found and destory , turning Chenle back into a kid, so he ended up going back to living with the his parents the Zhongs but now he & Jisung are closer in age only he's a year older. 

They didn't know why it happen but they were glad that it was over.

Jisung is still crushing on Chenle but it's ok cause now instead of a 11 year age difference it's now only a one year age difference.

End of flashback