。
I am truly very sorry for your loss.
Literal
Truly honorable-feeling's-poison [adverbial-に] humbly-know-[polite].
A heavily honorific/humble formal condolence. お気の毒 (lit. 'poison of [your honorable] spirit') is an empathetic set phrase for another's misfortune — 'pitiable, regrettable.' 存じる is the humble (kenjougo) verb for 知る/思う ('to know / to think'), here meaning 'I think/feel.' The combination お気の毒に存じます is one of the most formal ways to offer condolences — funeral-appropriate, stiff in casual contexts.