While once inseparable, Kate Middleton and younger sister Pippa are said to be on the outs as their lives "couldn't be more different," RadarOnline.com can reveal. With less than two years in age between them, Middleton, 43, and Pippa, 41, relied on each other as they navigated boarding school together and later the Princess of Wales' 2011 marriage to Prince William. But now sources claim new obstacles, including busy lives and raising children, have come between the sisters.Last week the UK press reported Middleton was forced to miss the fourth-grade party for Pippa's daughter, Grace, due to her work commitments. Instead of attending Grace's party, the Princess of Wales attended a Six Nations rugby match between England and Wales. An insider reportedly told New Idea the mother-of-three is "missing more and more of her old family" as her royal duties have ramped up.The source added: "Kate is painfully aware that things have been changing for awhile. The pressures of her public role have only increased since Queen Elizabeth passed away, pushing her husband and kids up the line of succession." They continued: "The unfortunate collateral of that has been losing the laid-back Middleton family way of things she holds so dear... especially her once close relationship with her little sister." Pippa, a mother-of-three married to financier James Matthews, also appeared to have retreated from her older sister's social circle.Middleton and Pippa, both major sports fans, were usually spotted attending Wimbledon together. But last they were spotted at a tennis match together, in July 2024, witnesses noted they looked tense. When Middleton made her shocking announcement she had been diagnosed with an unspecified cancer and was undergoing treatments just months earlier, her brother James, 37, issued a statement in support of her. Pippa, on the other hand, was oddly silent.While rumors of a sibling rivalry between the sisters have festered for years, a royal insider insisted "there has been no falling out between Kate and Pippa." The royal insider added: "I don't think that would ever happen. Of course there are sometimes issues between sisters, but they have always had each other's backs." Instead of a feud, the source suggested the sisters have "simply grown slightly apart" due to both being busy raising children.The insider added: "They both have three kids, but other that that their lives couldn't be more different. "Pippa and her husband are incredibly well-off and enjoy a private country life, whereas Kate is preparing her children to be the public faces of the monarchy. It's chalk and cheese. "I'm sure they still spend time together behind closed doors, but for not it seems Pippa has no interest in stepping back into the spotlight alongside Kate."