A body found in the River Ely is believed to be that of Ben Thompson, who went missing on 2 February after the Six Nations rugby tournament kicked off in Cardiff.
Thompson, 34, from Haverfordwest, had been to the Millennium Stadium to watch Wales play Ireland with a friend.
He was seen on CCTV crossing Leckwith Road in Cardiff at around 7.15pm, then turning to walk down a lane towards some wasteland.
Despite an extensive police search, there have been no further sightings of him since then.
It is thought he may have been trying to walk from the city centre back to his hotel near Cardiff Airport, about 12 miles away.
The body was found in the River Ely, which runs through Cardiff, yesterday afternoon and while formal identification is yet to take place, Thompson's family have been informed.
A police statement said: "South Wales Police can confirm that a body has this afternoon been found in the River Ely near Penarth Road.
"Formal identification has not taken place. The family of missing man Ben Thompson, aged 34, from Haverfordwest, has been informed and are being kept updated by family liaison officers."
Shocked and shaken
The body was found by a 26-year-old man from Cardiff whose boat is based at Cardiff Marine Village.
He told WalesOnline that the body was around 30ft from the river bank, saying he thought the body was a log at first: "We were driving off and the mechanic was looking at it, and said, 'what's that in the river?'
"So we said, 'shall we go and have a look?' We went back to the spot and saw it was a body.
"We told the mechanic and he said he would phone the police from the shore. We were shocked more than anything else. It's not something you expect to see. We were quite shaken up."
Prior to the discovery, a team of up to 50 officers were involved in the search for Thompson, and they had used sonar equipment to scour the river.
Last week, South Wales Police said: "Despite the skill, professionalism and best efforts of everyone involved we have unfortunately been unable to find Ben.
"Although daily searches of the river are no longer taking place, we will continue to do our best to find Ben with periodic searches over the coming weeks and months."