Dr. Robert Grossman was a 30-year-old neurosurgeon at Parkland Memorial Hospital in Dallas when President John F. Kennedy was rushed in with gunshot wounds Nov. 22, 1963.

Grossman served on a team of doctors who worked on and tried to save the president. Fifty years later, that tragic day has stayed with him, and become entwined in his family's history, as it did for others who were closest to Kennedy when he was shot.

Now, Grossman's 7-year-old grandson, William Oakley, who is in the first-grade, is fascinated by what happened in the emergency room that day with his grandfather and the president and asks endless questions. To help express his thoughts, he wrote a letter to President Kennedy, which he recited for "Nightline," from memory, as part of a special segment to mark the 50 th anniversary of Kennedy's assassination.

Watch the video here:

Watch the full story on "Nightline" tonight at 12:35 a.m. ET.