Who is the Fourth Apprentice?

everyones been wondering who's the fourth apprentice. Not much evidence suggests that Breezepaw is the fourth apprentice. I have found some evidence that Ivykit is the fourth apprentice though!
1. Ivy is the name of Vicky's niece.
2. the fourth apprentice will only be important starting the second book , Fading Echoes.
3. Ivypaw and Jayfeather are on the cover of Fading Echoes.
I have good reasons for Dovekit being the fourth apprentice
1. Dovekit is like Dove's Wing, Jay's Wing's sister
2. She is on the cover of the fourth apprentice.