Maybe the "royal rift" was over carbon emissions?

After Meghan Markle and Prince Harry came under fire for flying on private jets four times in just 11 days, Kate Middleton and Prince William were spotted taking commercial flights to and from Queen Elizabeth II's Balmoral Estate in Scotland.

Duchess Kate and Prince William spent $89 on their Flybe flight to Scotland from Norwich, England, last week, for which they were joined by their children: Prince George, 6, Princess Charlotte, 4, and Prince Louis, 1.

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”Earlier in the flight, I’d had the feeling that someone had come on the plane that I’d recognized — but I thought it was just a footballer,” a fellow passenger told The Sun. “We landed, and people then saw two black Range Rovers on the tarmac.

“Suddenly, Will, Kate and the kids all got up and left," the passenger continued. "They weren’t harassed by anyone at all as they got off the plane. They just seemed like a family traveling together, to be honest. No one saw them get on the plane either. It was amazing how they did it — they must have slipped on quietly after people were already seated.”

The family reportedly returned on a Loganair flight on Wednesday.

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Richard Pace, managing director of Norwich Airport, told The Eastern Daily Press of the royals' trip, "it's always a great privilege to welcome any member of the Royal family to our airport and we are always happy to welcome them."

Royal author Phil Dampier told The Mirror, "The contrast between William, Kate and family traveling on a cheap budget flight to Scotland and Harry and Meghan using private jets couldn’t be starker. A cynic might say the Cambridges have done it deliberately, bearing in mind the recent stories about the two brothers and their wives not getting on."

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"Harry and Meghan made a point of saying [they would] only have two children to save the planet knowing William and Kate have had three," Dampier added. "Could this be William and Kate hitting back?"

This month, Prince Harry, 34, and Duchess Meghan, 38, came under fire for flying private to and from a vacation to friend Elton John's estate in Nice, France, as well as to and from a getaway in Ibiza, Spain.

They reportedly flew from Farnborough, U.K., to Ibiza on Aug. 6, then back on Aug. 12.

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On Aug. 14, they flew from Farnborough to Nice, France, then back to Farnborough on Aug. 17.

The couple is believed to have taken a Gulfstream 200, which seats 19 people, to Ibiza from Farnborough, and a Cessna 500 XL, which seats nine, on their return trip.

The singer released a statement following the brouhaha, telling press, “I am deeply distressed by today’s distorted and malicious account in the press surrounding the Duke and Duchess of Sussex’s private stay at my home in Nice last week. Prince Harry’s Mother, Diana Princess Of Wales was one of my dearest friends. I feel a profound sense of obligation to protect Harry and his family from the unnecessary press intrusion that contributed to Diana’s untimely death.”

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"After a hectic year continuing their hard work and dedication to charity, David and I wanted the young family to have a private holiday inside the safety and tranquility of our home," he continued. "To maintain a high level of much-needed protection, we provided them with a private jet flight. To support Prince Harry’s commitment to the environment, we ensured their flight was carbon neutral, by making the appropriate contribution to Carbon Footprint™. I highly respect and applaud both Harry and Meghan’s commitment to charity and I’m calling on the press to cease these relentless and untrue assassinations on their character that are spuriously crafted on an almost daily basis."

PRINCE HARRY, KATY PERRY AMONG STARS ATTENDING GOOGLE CLIMATE CHANGE SUMMIT VIA PRIVATE JET

The trip to France reportedly had a carbon footprint of three tons, while the annual carbon footprint for the average British citizen is reportedly 13 tons.

The Ibiza trip is estimated to have emitted six times more carbon dioxide than a commercial flight from London to the Spanish island.

Prince Harry gave a speech barefoot earlier this month at Google's secret celebrity summit, saying he and Duchess Meghan would have, at maximum, two children (including infant son Archie) to prevent environmental harm from climate change.

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Prince Harry is said to have taken a private jet to the event, while Amal Clooney reportedly chartered a private jet in February for Duchess Meghan's star-studded baby shower.