Kate Middleton
Kate Middleton during a game of 'Three Tins' at the Commonwealth Games Village at the 2014 Commonwealth Games in Glasgow, Scotland July 29, 2014. Reuters

Britain’s Queen Elizabeth II made only a brief, 50-minute appearance at her great-grandson Prince George’s first birthday party July 22, and now we finally may know why.

According to a report from the Aug. 11 print issue of Life & Style magazine, the monarch’s longstanding distaste for the 32-year-old Duchess of Cambridge reared its ugly head again last month when Kate Middleton decided to concoct her own plans for her son’s birthday.

“[She’s] savoring a sweet personal victory over the queen,” reported the tabloid in their cover feature “Birthday Showdown! Kate Stands Up To The Queen.”

“She was raised in a very different way from her in-laws,” explained one “royal insider” of Middleton’s decision to hold her son's Peter Rabbit-themed soiree at Kensington Palace in London, directly defying the queen’s wishes to hold the celebration at her summer estate, Balmoral Castle, in Scotland.

“Kate wanted his party to be modern, fun and all about George,” said a source. “If he wanted to throw cake and ice cream around, she wanted him to be able to do it."

Queen Elizabeth, Kate Middleton
Britain's Queen Elizabeth and the Duchess of Cambridge, Kate Middleton, visit Leicester, at Kings Cross Station in London on March 8, 2012. Reuters

While successfully standing up to the 88-year-old Elizabeth may have been a small victory for Middleton, insiders report that her decision to host the party in London was also done in an effort to include her side of the family in on the celebration.

“Kate’s move made it easier for her family (including parents Carole and Michael, and siblings, Pippa and James) to enjoy the fun,” reported the tabloid.

Not only was Carole present for her grandson’s big day, she also reportedly helped Kate plan the themed affair. “Kate’s family is very close and wouldn’t have dreamed of missing Kate, Pippa or James’ birthday parties when they were little,” added an insider.

One party guest not thrilled by the Middleton family's presence? Allegedly, the queen.

“The queen looks down upon having commoners like the Middletons at royal events,” reported the magazine. “So, after a scant 50 minutes in the same room as them at the July 22 party … [she] left the palace.”

Even with the battle of Prince George’s birthday party behind them, insiders report that the royal duo are still at odds over how the presumed future king, and third in line to the throne, is raised. “The royals are used to putting work and duty first, but Kate doesn’t want that sort of life for herself or her family,” said a source.

Last month, Life & Style reported that the duchess and the queen have been secretly "at war" since 2011, when Middleton wed her grandson, Prince William.

“She feels very embarrassed by Kate,” said an insider, who claims that Her Majesty comments on everything about Middleton from her spending habits, to her clothing choices and even her parenting style. “She feels like she still acts like a commoner,” added a source.