A man has been arrested in connection with the stabbing of a man in Brighton on Sunday.
Abdul Deghayes, from Brighton, died in hospital in the early hours of Sunday morning after being stabbed in a car after it crashed.
Sussex Police has launched a murder investigation.
Abdul is the brother of two British teenagers killed fighting for Islamists in Syria.
The 22-year-old was found just before 9.30pm on Saturday in the passenger seat of a silver Volkswagen Polo which had crashed into other cars, police said.
He had a "number of stab wounds" and died from his injuries at the Royal Sussex Country Hospital, a spokesman said. Elm Grove, where the incident took place, remains cordoned off.
Abdul - who was jailed in 2017 for drug dealing - is the twin brother of Abdullah who was killed fighting in Syria in 2016 aged 18.
Their younger brother Jaffar, 17, was killed in 2014 while trying to overthrow Bashar Al-Assad's government.
Speaking at the time of Jaffar's death their father Abubaker Deghayes said his grief "cannot be described" as he claimed the Government was "criminalising" young Britons who have travelled to the war-torn country. (https://www.itv.com/news/meridian/update/2017-07-27/officials-in-brighton-failed-to-stop-terror-deaths-in-syria/) A serious case review published in 2017 found professionals missed opportunities to prevent the two teenage British Muslims being radicalised before they were killed after travelling to fight in Syria.
There was "no recognition" that Abdullah, Jaffar and their three siblings were becoming vulnerable to radicalisation in Brighton, the report said.
There was also little understanding of the part religion played in the lives of Abdullah and Jaffar, who were believed to have been with the al Qaida-affiliated Al-Nusra Front when they died, the review added.
A third brother, Amer Deghayes, a former finance student, also travelled to Syria in a bid to overthrow dictator Bashar Assad's government.