Board Thread:WARNING - SPOILERS and FALSE INFO AHEAD/@comment-208.181.121.162-20130715003225/@comment-138.130.66.226-20130718110618

I think there's two possibilities:-

1. They killed an Alpha merged as one so they both became Alphas but when they are not merged they only have half the strength of when they are which is why they do merge.

2. Both they're parents were Alpha's and when they died both of them became Alpha's.

3.(UNLIKELY) Their was only one and he was cut in half and healed as did the other side. - But since peter died getting his throat cut and Boyd died from being stabbed by claws, this scenario is EXTREMELY unlikely.