Paltrow was seen arriving at the star-studded event in Los Angeles with her rock star husband, Chris Martin.
While their friendship may come as a surprise, Paltrow and Aniston actually share a common past. Before marrying Martin, Paltrow was engaged to Pitt, whom she dated from 1994 to 1997. Aniston married Pitt in 2000, and they split in 2005. Aniston is now engaged to Justin Theroux.
Aniston's better known friends also attended Sunday's bash, including her "Friends" co-star Courteney Cox, who turned up with a mystery male companion.
Another Aniston pal, talk host Chelsea Handler, arrived solo.
Other notable attendees included Paltrow's "Iron Man" costar Robert Downey Jr. and his wife, Susan, "Arrested Development" stars Will Arnett and Jason Bateman, and "Spider-Man" star Tobey Maguire and his wife, star jewelry designer Jennifer Meyer.