、。
He'll be retiring next spring.
Literal
Next-year [possessive-の] spring, retire-honorific.
退職される is the honorific passive of 退職する — the passive form is the lighter, more distanced form of keigo (as opposed to the full honorific 退職なさる). This 'honorific passive' is very common in business and formal contexts for referring to a superior's actions without overt deference.