The family of one-punch attack victim Thomas Kelly has suffered its second tragedy in four years with the death of the teen's younger brother.
Stuart Kelly was 14 when his older brother died after being randomly punched while walking with his girlfriend in Kings Cross in July 2012.
The pair both attended The King's School at Parramatta, where Stuart was a prefect before graduating last year.
Headmaster Tim Hawkes said the school was shocked to hear about his death on Monday night.
"To have lost two sons in such circumstances is beyond awful," Dr Hawkes said in a statement.
"As a student, Stuart was greatly respected. The strength and character shown by Stuart when his brother was killed ... was extraordinary."
Eighteen-year-old Thomas had his life support turned off after being randomly attacked by Kieren Loveridge, who is serving a 10-year and two month jail sentence for manslaughter.
Last year Stuart delivered an emotional speech about the grief of losing his brother at a gala dinner for the Thomas Kelly Foundation, set up by parents Kathy and Ralph.
"I carry a deep scar that you cannot see. It's always there, it never leaves. It sits below the surface of your skin and surfaces when you least expect it."
At the dinner Stuart called on the NSW government to maintain its stance on lockout laws, to prevent more families facing the devastating consequences of senseless violence.
The lockout laws, introduced by the Baird government in 2014 after the deaths of teenagers Thomas and Daniel Christie, require most licensed premises in central Sydney and Kings Cross to refuse entry to patrons from 1.30am and stop serving alcohol at 3am.
Dr Hawkes said the school has offered support to Ralph and Kathy Kelly and their daughter Madeleine.
* For support and information about suicide prevention, call Lifeline on 13 11 14 or the Kids Helpline 1800 55 1800 or MensLine Australia 1300 78 99 78
