The live television audience was estimated at north of 35 million in the United States alone, although a time delay meant the actual obscenity was silenced.
"When I watched Kate (Winslet) two years ago, it looked so (bleep)-ing easy," she said, before covering her mouth and then pressing gamely on with the rest of her speech.
In the pressroom immediately afterward, Leo addressed the matter of her loose lips, saying: "Those words -- I apologize to anyone if they were offended. There's a great deal of the English language that is in my vernacular."
Leo was already a controversial nominee for her Oscars campaign, which included taking out advertisements on her own behalf. (Although we think it was quite hypocritical for anyone in self-promoting Hollywood to act like this was somehow out of line.)
One of her stated reasons for the campaign was to combat age-ism in Hollywood. Leo, 50, was offended that she was cast as Mark Wahlberg's mother even though she is only 11 years older.
Still, in that ivory lace Marc Bouwer number last night, she certainly looked like the mother of the bride kicking back her heels at her daughter's bachelorette party -- especially when she was swinging that Oscar around like an empty Champagne bottle at the end of the ceremony.
No doubt she had even more fun at the after-parties, where she didn't have to watch her language.
If you didn't get to experience Leo's slip up then you can check it out here in our partner video: