The younger brother of 'one punch' victim Thomas Kelly, 19-year-old Stuart Kelly, has died.
NSW Police have confirmed a 19-year-old-man was found dead in Mona Vale on Monday and a report will be prepared for the coroner.
The King's School school's headmaster, Dr Tim Hawkes, on Sunday night informed students and their families of Stuart's death, News Corp reports.
Stuart had completed Year 12 at the school last year.
"It is with great sadness that I inform you of the death of an Old Boy of the School, Stuart Kelly ('15). This is the second great tragedy to affect the Kelly family," Dr Hawkes said.
"The exact circumstances surrounding his death are not known, however, it is enough to know that we have lost a member of our community and therefore our thoughts and prayers go out to Kathy and Ralph Kelly and their daughter Madeleine."
Police believe there are no suspicious circumstances.
Stuart was just 14 when his older brother Thomas, then 18, died after being randomly punched by Kieren Loveridge as he walked with his girlfriend in Kings Cross in 2012.
Loveridge was convicted and sentenced to 13 years prison, with a non parole period of 10 years and two months.