Kate Middleton and Prince William broke royal protocol on their latest trip abroad for this reason

Prince William and Kate Middleton broke an important royal rule on Saturday, after jetting off with their three kids for the midterm break. 

• Prince William and Kate Middleton have broken a royal rule on their most recent trip—and it's not the first time it's happened. 
• The Duke and Duchess of Cambridge were spotted on Saturday at Heathrow Airport, the first stop on their well-deserved midterm break vacation. 
• In other royal news, the Queen is unable to walk her dogs for a week since being discharged from hospital stay.
  

Prince William and Kate Middleton may be the future King and Queen of England, but that doesn't mean they always do things by the book. The Duke and Duchess of Cambridge breached royal protocol during their most recent trip, evading one of the Queen's travel rules when flying with loved ones. 

With midterm now in full swing, the couple is enjoying a well-earned break from their busy schedules in London with their three children, George, Charlotte, and Louis. Photos of Prince William and Kate Middleton going on vacation with their kids and nanny at Heathrow Airport were snapped on Saturday, suggesting the aristocratic clan has traveled overseas for their latest holiday. 

While their country of choice remains unknown, it was initially rumored they flew to Greece to attend the wedding of their friend Prince Philippos and Nina Flohr. However, after failing to show face at the ceremony, the jury's still out on where exactly they've headed. 

The privileged family has previously treated themselves to some R&R at Amner Hall in Norfolk, as well as the Isles of Scilly and the Lake District. But by the looks of their light clothes at the airport, we're willing to bet they've opted for a sunnier spot this time around. 

If you're still scratching your head as to what royal rule they could have broken, you're not alone. Most people are unaware that members of the Royal Family are not technically allowed to travel on the same aircraft as each other, due to the risk of the lineage being wiped out in a crash. The Queen expects her younger relatives to split up when boarding a plane, and if they don't want to, they must ask her permission. 

Her Majesty famously granted special permission to William and Kate to fly to Australia in the same plane as Prince George in 2013, making an exemption due to the heir's young age. It seems the 95-year-old monarch has continued to show lenience with the rule, having now allowed her grandson and his family to share an aircraft on multiple occasions.  

"While there is no official rule on this, and royal heirs have traveled together in the past, it is something that the Queen has the final say on,” a BBC reporter explained in 2014. 

The reason behind Kate and Will's decision to fly on the same plane as their three children is pretty obvious—they're protective of them. Like many parents, the idea of letting their young kids fly solo (albeit with a nanny) isn't exactly appealing. The Duke and Duchess have also been known to keep George, Charlotte, and Louis out of the spotlight, and are best equipped to ensure their privacy if they're nearby at all times. Makes sense to us.