Although Kate Middleton is often photographed smiling, the Duchess of Cambridge appeared less than pleased when she traveled to Queen Elizabeth’s birthday celebration during Trooping the Colour.

Kate arrived at the celebration in the same horse-drawn carriage as Meghan Markle, Prince Harry and Camilla Parker Bowles. While some believed her “moody” attitude was directed at Meghan due to feud rumors, Kate was reportedly battling motion sickness.

“The truth is the Duchess of Cambridge gets very seasick and doesn’t enjoy the rocking motion of carriages. Worrying she may be ill on such an important occasion as Trooping the Colour added to her stress,” a royal insider told Mirror UK.

Like Kate, Queen Elizabeth also suffers from seasickness and has recommended medicine to the Duchess of Cambridge that previously eased her symptoms.

Unfortunately, Kate’s choice of medication is limited due to her public appearances. “The most effective drug makes you drowsy so wouldn’t be suitable for royals before a state occasion,” Dr. Qadeer Arshad from Imperial College London told the outlet.

Although Kate may not be able to ease her sickness during public appearances, Dr. Arshad revealed she could have more options in the future. “We’ve developed a technique using electricity to stimulate parts of the brain to ease symptoms.”

Despite her limited options, Kate was still able to enjoy her time at Queen Elizabeth’s celebration once she exited the carriage and joined Prince William, Prince George, Princess Charlotte, Prince Louis and the rest of the Royal Family to watch the air show.

Kate Middleton
Kate Middleton arrives to launch a new national support line at the charity Family Action on Jan. 22, 2019 in Lewisham, England.  Getty Images/Adrian Dennis