The Duchess of Cambridge's dour face said it all as she pulled into Kensington Palace Thursday. Yes, it's her 38th birthday, but no one in the royal family's in the mood for cake due to her bro-in-law, Prince Harry, and his wife, Meghan Markle, deciding to rock the royal boat one day earlier.

According to multiple reports, Queen Elizabeth, Prince Charles and Prince William are royally pissed off at Harry and Meg for going public with their plans to pull out of their Senior Royal duties and move, at least part-time, to Canada.

Word is QE2 told Harry to hold off on the announcement, but he defied Grandma ... and now there's talk he and Meghan could face some sort of punishment.

Meanwhile, poor Kate's like ... umm, it's my birth -- oh, never mind.

Hey, at least she looks happy in the official Instagram bday shot. That's something, right?

Fact is, Prince William and Prince Harry were already on the outs -- allegedly because Wills wasn't down with his decision to get married.

Now, William's gotta pull his wife's bday celebration out of Harry's fire?? Good times.