Prince William's off-the-cuff response to Prince Harry and Meghan Markle's interview with Oprah Winfrey caught some royal fans off-guard. 

On Thursday, William responded to a reporter who asked two impromptu questions while he and Kate Middleton were visiting a London school. The Duke of Cambridge's remarks seemed to be referencing the moment in Meghan's talk with Oprah when she claimed that a member of the royal family had "concerns and conversations about how dark [her and Harry's son, Archie's,] skin might be when he's born." 

"We are very much not a racist family," William told the reporter, adding that "I haven't spoken to [Harry] yet, but I will."

Royal expert Katie Nicholl tells ET that while what he said holds great significance, how he said it is most surprising. Nicholl points out that it's very rare that any member of the royal family responds to a reporter in such a casual manner. In fact, it's usually seen as disrespectful for the press in the United Kingdom to shout questions out to the royal family while they're on engagements. However, this has been happening more often following Meghan and Harry's tell-all interview. 

"It was very unusual for Prince William to answer. I mean, Prince Charles was on an engagement earlier this week, and a member of the press called out ...[and] Prince Charles didn't comment -- [but] William did," she shares with ET. "He answered not once, but twice. I think that's very telling of his mood at the moment."

Nicholl also notes that William is known for being "a consummate professional when it comes to being on engagements."

"He's done this for a very long time and I think he was probably very prepared for a question to be asked," she adds. "His answer was pretty to the point, it was pretty swift, it was very much off-the-cuff."

Nicholl further emphasizes how rare it is that a royal, especially William, would give such an unrehearsed comment.  

"The fact that he answered two questions was really very, very unusual. I think highly significant," Nicholl says, adding that she's told by sources close to William that he is "beyond livid over [Meghan and Harry's] interview." 

"I think he wanted the chance to say something," she notes.

As for why William spoke out, Nicholl says, "...He feels that he has to defend his family, and that's what he did today."

Both Harry, 36, and William, 38, have admitted that they've not spoken to one another in recent days, and Nicholl doesn't expect them to rekindle their brotherly bond overnight. 

"I think everyone hopes that the brothers will be able to heal this rift, clearly it does run deep. I think it speaks volumes that William hasn't yet picked up the phone to call his brother. I think that he's clearly needed some cooling off time," she explains. "...I think the feeling though is that time is a healer. That's something that Harry himself said."

One of the soonest times the brothers could reunite would be at the unveiling of Princess Diana's statue on July 1 in the Sunken Garden at Kensington Palace, where their late mother would often visit. 

"[Diana] said she always wanted her boys to be close, and I think people saw an unbreakable bond between those boys," Nicholl says. "Things have come to blows, the relationship is clearly under a lot of strain, but hopefully behind closed doors that can begin to heal."

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