Question re "Mark Evans"

[sbursztynski]

No: HPFGUIDX 104734

I am puzzled at frequent references to 10-year-old Mark Evans as a relative 
of Harry's. Where, in canon, does it say this? Has JKR said it? If so, why are 
we told, time after time, that Harry's only relatives are the Dursleys? To be 
more precise - that Petunia is his mother's last remaining blood, the reason 
for the spell to protect him. Maybe I missed something somewhere? :-) If I 
have, and ME is a relative, why doesn't Harry seem to know this? Who is 
ME's Dad - a brother or cousin of Lily and Petunia? And why don't the rellies 
come over to complain about his being bashed up by Dudley? And why was 
Harry left with the Dursleys, horrible as they are, if there was another 
alternative?

Evans is a common name - is there any reason why he has to be related? 

Just a  few questions - if someone can point me in the right direction, I'll be 
happy . ;-)