I think Morgana told Uther and Ygraine about Arthur's boyfriend from college, Merlin, who he had to leave behind. During the parade, I think Morgana sees Merlin in the crowd and tells Arthur. Everybody else in the family tells Arthur to go and get Merlin and bring him to them. I'm pretty sure Arthur jumps off the float, runs towards Merlin they hug and it's super fluffy. Arthur takes merlin back to the float and introduces him to the family.
Other details I remember:
- The oc sister ate a lollipop at some point.
- Uther is nice
- Ygraine is alive.
- It might have been part of a series.
Someone, please help, I been looking for this for over a year
Edit: It might have been on Fanfiction.net, I'm not really sure...