First Minister Mark Drakeford has announced plans for an M4 relief road have been scrapped.
In a letter signed by the First Minister, he said he did not see a ''compelling case in the public interest'' for the scheme.
The proposal was for a second motorway to the south of Newport, parallel to the existing M4 motorway from junction 23A at Magor, to junction 29 at Castleton, avoiding the need to widen the Brynglas Tunnels.
Supporters say it is needed to ease traffic congestion in the area.
But the First Minister took concerns over the environmental impact of the scheme into consideration and its impact on the nearby Gwent Levels.
Timeline of events:
An M4 relief road was first proposed by the Wales Office in 1991, but there was little progress in the following years.
Plans for the new M4 were announced in March 2006, but in July 2009, the Deputy First Minister Ieuan Wyn Jones announced that the plans were to be dropped.
In March 2012, the Welsh Government launched a consultation on plans that could ease congestion on the M4 around Newport.
A public consultation exercise opened in March 2012.
In 2014, Wales Transport Minister Edwina Hart said that the preferred "black route" south of Newport between Junctions 23 and 29, including a new crossing of the River Usk, would go ahead.
In 2017, a public enquiry was launched to look at the £1.3 billion pound project and its economic impact, environmental and social factors too. It looked at evidence relating to 22 possible alternatives to the 'black route'. During the inquiry, the Welsh government announced that the road will cost an extra £136 million and the opening would also be delayed by two years.
In October 2018, AMs were told they will have a "binding vote" on whether to build an M4 relief road before First Minister Carwyn Jones stands down in December.
June 2019: Plans scrapped
Before the announcement, we spoke to those on both sides of the argument to hear their views:
Reacting to the news, the director of the Confederation of British Industry described it as a ''dark day for the Welsh economy.''
Andrew RT Davies called for Transport Minister Ken Skates to resign.
Plaid Cymru, who were against the plans, welcomed the news stating that it would have been ''environmentally damaging'', but criticised the Welsh Government for the cost in delaying the decision.
Plaid is now calling for the £1.4 billion funding earmarked for the project to be reinvested in Wales' transport network. Shadow Economy Minister, Rhun ap Iorwerth AM, says the money could go towards "the development of a long-term vision for a green and sustainable" Welsh transport network.
He added: "Newport may be the focus of our transport woes but it can also be the catalyst that provides a solution to the transport woes for the whole of Wales".