EXCLUSIVE: Why Kim Richards Missed Nicky Hilton's Epic Wedding

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Nicky Hilton's wedding to banking heir James Rothschild on Friday at Kensington Palace in London was quite the lavish affair, but one person was noticeably absent from the festivities -- her aunt, Real Housewives of Beverly Hills star Kim Richards.

A source tells ET that, "Kim was invited to the wedding, but she decided not to go." Kim, who entered rehab for the fourth time in April after being arrested at the Beverly Hills Hotel for intoxication, is currently "focusing on her sobriety and her health," the source adds.

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The 50-year-old reality star's younger sister and fellow RHOBH cast member, Kyle Richards, was in attendance at Friday's nuptials. Kim and Kyle are sisters of Kathy Hilton, Nicky's mother.

Kim did leave rehab briefly in May to attend her daughter Brooke Brinson's wedding to Thayer Wiederhorn in Cabo San Lucas, Mexico. In June, ET confirmed that she will not be returning to RHOBH next season.

"[But] she is much better than she had been," a source told ET at the time about Kim's current state.

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Kim has been on the hit Bravo show since its first season in 2010, and has been open about her battle with alcohol addiction in the past. Watch the video below for more on her season six exit.

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