Alex and Dana, being siblings, share the same parents. Blake's mother being the sister of Alex and Dana's father means that Blake is their cousin. Since Blake's mother is the sister of Alex and Dana's father, Charlie, being a cousin at the reunion and an only child whose mother is not mentioned as the sibling of either Blake's mother or Alex and Dana's father, must be the child of another sibling of Alex and Dana's father. Consequently, Charlie is also the cousin of Alex, Blake, and Dana. 

Charlie's relationship with Blake's mother is that of a niece or nephew, since Blake's mother is a sibling to one of Charlie's parents. Alex's father is Blake's uncle, given that Blake's mother is Alex's father's sister.
At a family reunion, there are four cousins: Alex, Blake, Charlie, and Dana. Alex and Dana are siblings. Blake's mother is the sister of Alex and Dana's father. Charlie is an only child, and their mother is not at the reunion. Who is Charlie related to, and how? What relationship does Charlie have with Blake's mother? What is the relationship between Alex's father and Blake?
Provide a very brief response.