The couple, which has been dating since meeting on the set of the U.S. vampire drama in the summer of 2007, announced its engagement last month (Aug09).
The stars have yet to set a date for their nuptials, but Moyer reveals he's already appointed his border collie to the top role - choosing his furry friend over his young son, Billy.
He says, "We haven't planned anything. (But) Splash, my alpha, will be the ringbearer. My son might be unhappy about that!"
Billy, born in 2000, is Moyer's child from a previous relationship. The actor is also father to daughter Lilac, who was born in 2002.