He was Jack Murnin, a native of Downpatrick.
The crash happened on the Strangford Road in the town around 1 pm.
It is the second road tragedy to his the Murnin family in th past 15 years.
SDLP South Down MP Margaret Ritchie said: “This loss is all the more poignant at this time of year and considering that his father passed away under similar circumstances 14 years ago.
“Jack and his father are survived by his mother, grandmother and two siblings, whose grief must be beyond reckoning.”
Meanwhile, a 19-year-old man has been critically injured in an accident in Lisburn.
He was a passenger in a car that crashed on the Hillhall Road in the city just before 2 pm.