@MisterMoo What in the world are you talking about? His surname Griffiths is singular so it takes ‘s to make possessive. Some style guides make exceptions for “biblical names”, by which they mean “Jesus” and “Moses”, but that’s dumb.
@gruber @MisterMoo Not that it's the Bible or anything, but you're throwing the AP Stylebook out the window here, my dude.
For singular proper names ending in s: Use only an apostrophe.