what if I found out my fiance's first kid might not be his?

so here's the thing back in like late 2008 early 2009 I used to hang out with my fiancee. and then for whatever reason we fell apart and he hooked up with this girl who is now his ex wife. either way his first born child was born mid may 2009. and I was looking through on Facebook some of his old pictures and I come across our first picture together. which was dated Feb 25th 2009. so idk if maybe it was a late upload or what exactly but does it seem like she his ex might of claimed him to be the dad when he might not of been. or could this just be a Facebook error? question is do I tell him?