(CNN) When Navy ensign Sam Bongiorno opened his mailbox on Monday, he found an envelope he never expected to see: a letter from the late Sen. John McCain.

McCain had written to congratulate him on his recent graduation from the Merchant Marine Academy. The letter, written on August 20, was mailed on August 25 from McCain's Phoenix office.

"I graduated in June, but never expected to hear from him or his office due to his declining health," he told CNN. McCain himself graduated from a service academy: the Naval Academy.

"I commend you for your decision to serve our nation," McCain wrote in the letter. "It is young people like you who make the future of this nation brighter and stronger."

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