Harry's Grandfathers - one still alive? (LV or DD??)

[medeacallous]

No: HPFGUIDX 61386

I searched through the archives and I couldn't see my specific 
question, although I know the Dumbledore/Voldemort theory has been 
done to death.

My theory is that one of Harry's Grandfathers is still alive, and 
the basis is from page 156 of the Canadian edition of HP:PS, the 
Mirror of Erised chapter.  The phrase is something like '...one of 
Harry's grandfathers was smiling happily.'

One conclusion is that while both Grandfathers were dead and 
observed in the Mirror, only one Grandfather was described.  But 
what if the phrase is indicating that only one of Harry's 
Grandfathers is actually dead?  If so, is it Lily's dad?  Where and 
who is he??

Sorry if I'm repeating something that's already been discussed.

MC