Robert De Niro, Girlfriend Tiffany Chen Hit Cannes Party After Having New Baby

Robert De Niro's got a lot to celebrate these days -- not only has he debuted his new flick at Cannes, but he's a father once again ... and the mother to baby #7 joined him in France for a bash at the prestigious film festival.

The 79-year-old actor and his GF Tiffany Chen hit up the Vanity Fair x Prada party Saturday night at Hotel du Cap-Eden-Roc, and he looked as happy as ever as they strolled in for some late-night festivities.

Just hours before, Robert premiered his new Martin Scorsese-directed film, "Killers of the Flower Moon" ... getting an enormous roar of applause and a nine-minute standing ovation for the new movie -- which he stars in alongside Leonardo DiCaprio, Jesse Plemons, and breakout star Lily Gladstone.

As we reported, Robert and Tiffany welcomed their new daughter -- Gia Virginia -- earlier this month, shocking tons of folks while proving age is but a number.