On stage eight of the race in Sicily there was an accident involving car number 15, Breen and Roberts, which resulted in the stage being stopped to enable medical crews to attend the scene.
Despite their best efforts, Roberts succumbed to his injuries and the remainder of the event has been cancelled as a mark of respect.
Breen was unhurt in the accident but treated for shock at the scene. No spectators were involved.
Eurosport joins the IRC community in offering its sincere condolences to Gareth’s family and friends, who are in our thoughts at this sad time.
Gareth, who was 24 and from Wales, trained as an electrician.
He began competing in 2004 and achieved considerable success in the one-make Fiesta SportTrophy series. He formed a formidable partnership with Breen for the start of the 2009 season, which included the pair winning the inaugural FIA WRC Academy Cup in 2011.
Roberts was embarking on his first major campaign in the IRC. Following points-scoring finishes on the Donnelly Group Circuit of Ireland Rally in April and Giru di Corsica-Tour de Corse last month, their programme with Sainteloc Racing would have included the upcoming Geko Ypres Rally and Sibiu Rally Romania.
Their participation on Targa Florio-Rally Internazionale Di Sicilia with HRT Motorsport was added to their schedule to provide an additional opportunity to demonstrate their considerable talents in a Peugeot 207 Super 2000.
After seven stages in Sicily they were in sixth position overall having set a succession of impressive stage times on an event they were competing on for the first time.
Following their performance in Corsica, where an onboard camera captured Gareth’s expert pacenote-reading skills live on Eurosport, Breen said: “Gareth is a magician, he’s incredible how he gets every note out so quickly. I couldn’t do it without him.”
"It's a very sad accident that reminds us that motorsport is dangerous," IRC manager Jean-Pierre Nicolas said.
"Accidents can affect both driver and co-driver in rallying, and sadly, more often than not it is the co-driver who suffers - as we saw in 2005 on Rally Great Britain when Michael Park was killed.
"The death of a 24-year-old young man at the start of a fantastic career is always a tragedy.
"At this terrible time, I'm thinking very much of Gareth's family."
The remainder of the event has been cancelled as a mark of respect.