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How Meghan Markle Is Spending Coronation Day with Birthday Boy Prince Archie and Princess Lilibet

While the royal family (including Prince Harry) marked King Charles and Queen Camilla's coronation on Saturday, Meghan Markle was back home in Montecito, California, ringing in son Prince Archie's fourth birthday.

As she's done in years past, the Duchess of Sussex, 41, planned a laid-back celebration at home for her young son with close friends and family.

"It's going to be a low-key party at home," a source told PEOPLE. "They'll have friends around them and Meghan's mom, Doria [Ragland]. Meghan will definitely have support that weekend."

And Archie will have his little sister, Princess Lilibet, 23 months, by his side.

"They are so sweet together. Archie loves Lili. He's such a sweet boy. When she's not around, he asks, 'Where's Lili?' " the source added.Meghan's decision to stay back in California while Prince Harry attended his father's coronation reflects the complex feelings between the couple and the royal family.

"Things are strained," says a palace insider.

Those closest to the couple know that the media backlash Meghan faced in the U.K. during Queen Elizabeth's funeral last year — and in the seven months since — played a significant role in her decision not to come.

"Meghan wants to be there to support her father-in-law, but at the same time, the scrutiny she receives outweighs the support," the close friend says. "There's always going to be that other side challenging their reasoning, and who wants to put themselves in that position?"

Prince Harry arrived at Westminster Abbey for the crowning ceremony on Saturday with his cousins Princess Eugenie and Princess Beatrice, joined by the sisters' husbands. After chatting with Beatrice's husband, Edoardo Mapelli Mozzi, on the walk inside, Harry talked with Eugenie's husband, Jack Brooksbank, who he sat beside in the third row during the service.

The Duke of Sussex wore a morning suit for the occasion, following the dress code for most of the congregation. PEOPLE understands Harry was requested to wear a morning suit — and that he didn't make any specific asks regarding his outfit. He adorned the suit with his Afghanistan service medal along with the Golden Jubilee, Diamond Jubilee and Platinum Jubilee medals as well as his KCVO neck decoration and star.Prince Archie and Princess Lili were last in the U.K. during Queen Elizabeth's Platinum Jubilee celebrations in June 2022. The significant trip was Princess Lili's first visit to the U.K., as she was born in California on June 4, 2021, and had yet to visit her dad's homeland. Archie was born in the U.K. on May 6, 2019, but hadn't been back since late 2019.

During the Duke and Duchess of Sussex's time in the U.K. last June, they held a small birthday party for Lili, who turned 1 during the trip. The couple, who relocated to Meghan's home state of California after stepping back from their royal roles in 2020, invited close friends and family to gather for a "casual, intimate backyard picnic" at Frogmore Cottage, a spokesperson said.

Fans got another glimpse of the festivities in the Netflix docuseries Harry & Meghan, which aired in December 2022. The Duke and Duchess of Sussex shared intimate family photos throughout the six-episode series, including from Lili's birthday party.Upon the death of Queen Elizabeth in September, Harry's father became King Charles — and as grandchildren of the monarch, Archie and Lili were afforded the titles of prince and princess.

"The children's titles have been a birthright since their grandfather became monarch," a spokesperson for the Duke and Duchess of Sussex told PEOPLE. "This matter has been settled for some time in alignment with Buckingham Palace."