An MP who took part in a Nazi-themed stag party organised the event and bought an SS fancy dress uniform, a Conservative Party report has confirmed.
The exact details of Aidan Burley's level of involvement in the party had been unclear since it took place in France at the end of 2011.
But the Tories concluded their Cannock Chase MP had been "stupid and offensive" for leading the stunt in a ski resort.
The session included party-goers and friends of Mr Burley dressing up as SS officers, toasting the Third Reich and chanting the names of senior Nazis.
Mr Burley's friend, Mark Fournier, was handed the maximum fine of 1,500 euros by a French court on Tuesday. Mr Fournier, the groom, had been photographed wearing the SS outfit and giving a Nazi salute.
The Conservative report was written by peer Lord Gold in the months after the incident, but was only revealed yesterday after the court imposed the fine.
The report concluded: "Mr Burley is not a bad man, still less a racist or antisemite. However, his actions were stupid and offensive."
It is not yet clear what further action will be taken against Mr Burley, who was sacked as a Parliamentary private secretary after details of the party came to light.
Mr Burley said last month: “I told the JC two years ago that I deeply regretted the incident and that remains the case."
He has not yet commented on the results of the party report.