Robert Pattinson and Kristen Stewart smooch at premier post-party

Well this is something that we never see: Robert Pattinson and Kristen Stewart sharing a steamy kiss!

Since the "Twilight" costars first hooked up in 2009, they've done their best to keep their real-life relationship under wraps. However, the cautious couple let their guard down at a Cannes Film Festival party on Wednesday night, sharing an epic liplock and too-cute-for-words cuddle on a balcony.

This rare public display of affection took place at an afterparty for Stewart's upcoming film "On the Road," which premiered earlier that night. Pattinson, 26, attended the event to support his lady love, but they walked the red carpet separately and didn't pose for photos together. In the screening, he was seated a row away from Stewart, 22, who was grouped near her costars.

It was at the post-premiere party that they enjoyed their intimate moment. Standing alone together on the balcony, they had their arms around one another's necks in an embrace before they kissed. He also planted a sweet smooch on her forehead. Then they stood together laughing and smiling.

Stewart and Pattinson have masterfully deflected questions about their relationship over the years. She will sometimes mention him in an interview, like she did recently in Elle, referring to him simply as her "boyfriend." However when the magazine asked if marriage was in their future, she said, "Everyone wants to know. Everyone knows already—it's ridiculous," without answering the question.

As for Pattinson, he coyly deflects questions about his on-screen love interest as well, but recently made hearts melt with a sly mention of love. When a reporter from Vanity Fair Italy asked the 26-year-old about the best compliment he's ever received from a woman, he said: "The most beautiful thing a woman can tell you is that she loves you."

We wonder if Kristen was whispering that in Robert's ear on the balcony.