Kate Middleton stammered for words in a televised interview when asked if she could measure up to the legacy of the late Princess Diana. Prince William sensed her nervousness and offered reassurance -- speaking to the camera, but indirectly speaking to his bride-to-be.

"It's about carving your own future," he said. "No one is trying to fill my mother's shoes. What she did is fantastic. It's about making your own future and your own destiny and Kate will do a very good job of that."

The moment was exciting for Maryhope Howland, a researcher and PhD. student in social psychology at the University of Minnesota. First, she's a self-described "huge fan of the royals" who has been glued to the media coverage of the upcoming wedding. Second, this subtle exchange exemplified a concept called "invisible support" that she has found through research to contribute to healthy relationships.

"It's basically providing support in a way that doesn't look or feel like traditional support," she said. "He didn't turn to Kate and say, 'no pressure, you'll do great.' He said it to someone else."

Scroll to 12:40 on this clip to see the moment:

In a study published last November, Howland and colleagues surveyed 85 couples before and after interviewing them. Those couples who exhibited signs of invisible support during the interviews felt less anxious and more satisfied with their relationships at the end.

What is invisible support exactly? Howland likened it to "giving someone a supportive idea without necessarily directing the person to do one thing or another." Watch this two minute video for more details on the concept.

Why invisible support works is somewhat unclear. (It's called invisible because it only works if the receiver of the support doesn't identify it.) Traditional support can often come with hurt feelings, Howland said. People receiving support might feel inadequate or they might resent that their spouses or partners are providing support in the form of advice (telling them what to do).

"It might be when we provide support very directly we are conveying a message of a lack of confidence in that person," Howland said.

Howland stressed that invisible support is only useful in moderately stressful situations, such as bad days at work. Direct support is much more appropriate in instances of major stressors such as family deaths.

Many wonder if this royal marriage will endure -- given the troubled marriages of Prince Charles and Diana, and Prince Andrew and Fergie. While research does not indicate whether invisible support produces longer relationships, Howland nonetheless said it was a good sign that Prince William was capable of this kind of subtle support for Kate during the TV interview.

"Assuming she didn't really catch on that he was supporting her, then according to my research, I would have expected her to have left that interview feeling less anxious and more confident of her ability to go into that situation" of joining the Royal Family, Howland said.

"If this is how he does it on a day to day basis," Howland said, "then I think that bodes well."