(I) beg your pardon, but...
and Begging your pardon, but...Please excuse me, but. (A very polite and formal way of interrupting, bringing something to someone's attention, or asking a question of a stranger.) Rachel: Beg your pardon, but I think your right front tire is a little low. Henry: Well, I guess it is. Thank you. John: Begging your pardon, ma'am, but weren't we on the same cruise ship in Alaska last July? Rachel: Couldn't have been me.