The crash happened at the second Severn Crossing.
The M4 second Severn crossing has now reopened in both directions after a lorry left the road and crashed yesterday morning.
Officers responded to a call at 10.30am on Wednesday to a report a lorry had left the carriageway and gone down onto the embankment and onto land alongside the M4 Westbound at the end of the Prince of Wales Bridge.
The driver of the HGV was airlifted to the University Hospital of Wales in Cardiff but died of his injuries,
Gwent Police are appealing for any witnesses or those with dashcam footage to get in touch.
They're urged to contact Gwent Police on 101 or Direct Message us on Facebook or Twitter, quoting log 129 04/09/19.