ITV Wales understands that Rhodri Morgan collapsed and died while cycling in the lanes near his home.
South Wales Police say officers were called to an incident involving the former First Minister in the Wenvoe area shortly after 5pm on Wednesday evening.
Officers and paramedics went to the scene after reports that a man had been taken ill, but say Mr Morgan was pronounced dead at the scene.
Friends have told ITV Wales "he died doing what he loved".
The coroner has been informed.
The wife of the former First Minister Rhodri Morgan, who died on Wednesday at the age of 77, has appeared at a tribute to her husband.
Friends, fellow politicians and journalists have been sharing their favourite memories of him.
A brief look back at Rhodri Morgan's political career following the news of his death.