Prince Harry and Meghan Markle could find themselves at odds with each other if Prince William decides to invite them to his and Kate Middleton's joint birthday bash at Windsor Castle.

The Duke and Duchess of Cambridge are planning to have a joint birthday celebration this summer either at Windsor Castle or Sandringham. According to reports, the duchess is interested to have the Duke of Sussex over as it would really mean a lot for her husband if his younger brother is there.

However, this could cause tension or friction between the 37-year-old and his wife. Speaking on his YouTube channel, royal commentator Neil Sean said, "That big party, which we believe will be held at Windsor Castle, could create a few problems."

He added, "It does appear that there's a bit of shall we say friction between Prince Harry and Meghan Markle according to a very good source, and as ever we have to say allegedly."

Sean claimed that Prince Harry would be open to the idea of returning to the U.K. for Prince William and Kate Middleton's birthday bash. However, Meghan Markle may not be so keen to travel again given that they were recently in the U.K. for the Platinum Jubilee celebrations. They also have two children to take care of in California.

"But according to that good source, Meghan Markle is not keen at all to go back into a room, some might say a hornet's nest of which she did her own stirring, to spend an evening, afternoon, day, whatever that might be celebrating someone who clearly has got issues with her and likewise vice versa," he shared.

Sean thinks that the Duke of Sussex may want to be at the party for the sake of his brother. He explained, "Prince Harry of course now 18 months, two years down the line is probably looking back at his life and thinking to himself, 'this is something I truly do want to celebrate, he is my brother', and they were good and close."

Prince William turned 40 years old on June 21 and Kate Middleton had her birthday earlier on Jan. 9. Prince Harry and Meghan Markle recently celebrated the first birthday of their daughter Lilibet on June 4 at Frogmore Cottage.

Meghan Markle, Prince Harry and Prince William
Prince Harry last revealed that he had grown apart from his older brother William Photo: AFP / Tolga AKMEN