Actor/director Ryan Gosling partakes in 'A Conversation With Ryan Gosling' during 2015 SXSW Music, Film + Interactive Festival at Austin Convention Center on March 13, 2015, in Austin, Texas Getty Images/Michael Loccisano

AUSTIN, Texas -- Ryan Gosling, star of “Drive” and “The Notebook,” wasn’t the only one enjoying a once-in-a-lifetime moment at the South by Southwest Film Festival Saturday night. At the North American premiere of Gosling’s directorial debut, “Lost River,” one woman used the microphone during the post-movie question-and-answer period to propose to her partner.

After the “Lost River” credits rolled, Gosling and members of the cast such as his own partner Eva Mendes, Ben Mendelsohn and Saoirse Ronan took the stage to answer questions posed by audience members. The session was relatively routine, until the final question of the night: Instead of addressing Gosling or his cast members, Heather MacKay turned to her partner Susan Dion and asked whether she would marry her.

“To be very honest, the proposal was very spontaneous,” MacKay said. “I just had the ring in my pocket so that I would be prepared if the moment presented itself. I did not expect that moment to be at the premiere [of ‘Lost River’].”

MacKay added: “I felt the ring box shift in my pocket while I adjusted in my seat right after Ryan Gosling and his cast started answering questions from the audience. I contemplated doing it during the whole Q&A; I was unsure if it was appropriate or not.” Then she took a hint from the famous couple onstage. “After Eva Mendes made a comment about being a big fan of Ryan’s and everyone started laughing, I decided that I would raise my hand towards the end. I figured that if I was chosen to ask a question that it would be a sign and I should go for it.”

Like many other audience members attending the star-studded premiere of “Lost River,” MacKay and Dion are big fans of Ryan Gosling. “Susan and I joke that he is my man crush. [Gosling] is significant to us because of his movie, ‘The Notebook.’ It came out shortly after we started dating in 2004, and it became ‘our’ movie. We are not movie buffs, or celeb fans, but we think it's very interesting that a movie captured our lives so perfectly well.”

When Gosling realized that this was no typical fan question, he offered the mic to MacKay so she could properly finish her proposal. The couple had gone through several periods of estrangement before reuniting in Austin, and MacKay shared their story as curious audience members and the “Lost River” cast looked on. When Dion said, “Yes,” the crowd erupted into cheers.

“Well, let’s go out on that note, shall we?” Gosling said as he closed the premiere of “Lost River” and heralded the beginning of a new chapter in MacKay’s and Dion’s life.

MacKay posted the video of the engagement the next morning and thanked the “Lost River” crew afterward:

Just another memorable night at SXSW.

“Lost River” opens in theaters and via video-on-demand services April 10. The SXSW Film Festival runs March 13-21.