It was double the love in New York City on Tuesday night.
Mary-Kate, 28, slipped into the theater hand-in-hand with her fiancé Olivier Sarkozy, 45, while Ashley, 28, left red carpet duties to Miller as she snuck past with a female friend.
At the afterparty at the Standard Hotel, Ashley continued to play the part of the supportive plus-one.
Dressed in a long, flowy dress, she was an early arrival, chatting with her pal as they awaited Miller’s arrival.
Once he walked in, “she gave him a really long embrace. It was a really sweet, long hug with her arms wrapped tightly around him,” a partygoer at the bash (which was sponsored by Details and Patron tequila) tells PEOPLE.
Throughout the night, their PDA continued. At one point, “they were standing in a group and were locked in a hug with him rubbing her back,” the partygoer says.
In another tender moment, “Ashley put her head on his shoulder. She was really sweet.”
The two have plenty to celebrate. The film – based on a true story and starring Steve Carell, Channing Tatum and Mark Ruffalo – is getting early Oscar buzz. Tatum and Ruffalo play two wrestler brothers whose lives are ripped apart when a wealthy benefactor (played by Carell) develops obsessions that result in tragedy.