Edouard Baer was with Depardieu on the Dublin-bound flight, when the Cyrano de Bergerac star relieved himself into a bottle after stewards informed him that he couldn't use the restroom prior to take-off.
Depardieu was escorted off the flight by security when urine leaked onto the floor.
Baer has now insisted that the French film icon is sorry that his prostate ailment caused a disturbance for other passengers.
Baer said in a statement: "Gerard is very sorry for what happened. He wanted to go to the toilet but he was forbidden because we were about to take off, so he was forced to do it on the plane in front of everybody. I found the solution by passing him a mini Evian water bottle, but it was too small and overflowed.
"He has prostate problems and it was very worrying and humiliating for him. He was also stone-cold sober at the time. This is not the way he usually behaves."
Airline City Jet joked about the incident in a series of Twitter posts on Wednesday: "As you may have seen on the news, we are busy mopping the floor of one of our planes this morning...
"We'd also like to remind all passengers that our planes are fully equipped with toilet facilities..."
Depardieu most recently starred opposite Catherine Deneuve and Jérémie Renier in François Ozon's comedy Potiche, which opened in March in the US.
> Depardieu 'admits smashing parked car'
Watch the Potiche trailer below: