France's hopes of defending their RBS 6 Nations crown evaporated in a 10-minute spell at home to eventual champions Wales, according to national team coach Bernard Laporte.
Laporte's men produced an inconsistent set of performances, with two unconvincing wins over Scotland and England and two impressive victories over Ireland and Italy.
However, in their third match of the tournament they faced Wales at the Stade de France.
Laporte believes that this contest decided the destination of the championship trophy.
Les Bleus slumped to a 24-18 defeat to the Welsh, who finished top of the RBS 6 Nations table, one place above France.
"We regret the first 10 minutes of our second half against Wales where we lost the match and the Grand Slam, when I look back," said Laporte.
"It is difficult to accept this loss. Without those little moments of poor concentration we would have cried tears of happiness on Saturday."
Despite a flawless first-half display against Wales, the French failed to capitalise on their 15-6 half-time advantage and conceded two tries in the first six minutes of the second half before tumbling to defeat.
Wales went on to clinch their first Grand Slam since 1978 with a 32-20 win over Ireland at the Millennium Stadium on Saturday.
And Laporte was quick to congratulate Mike Ruddock's team on their triumph.
"This is somehow a tournament of regrets for us but on the other hand the Welsh showed their qualities that day and their Grand Slam is thoroughly deserved."
As head coach Stuart Lancaster polishes the axe he will soon wield over his World Cup training squad, Exeter Chiefs coach Rob Baxter has backed Jack Nowell, Henry Slade and Luke Cowan-Dickie to be given a stay of execution.
Italy Under-20s held off a late Samoa blitz to retain their place in the World Rugby U20 Championship on Saturday and head coach Alessandro Troncon believes the experience will have served as a valuable lesson for his young troops.