。
Would you mind telling us the truth?
Literal
True [possessive-の] thing [object-を] say-[honorific-おっしゃって] receive-[humble potential-いただけませんか]?
おっしゃる is the honorific form of 言う ('to say'). ~ていただけませんか ('would you be so kind as to') is one of the most polite request forms — combining humble いただく with the potential negative question. The combination of honorific verb + humble request is maximally deferential.