Former Big Brother housemate Claire Rehfuss is addressing rumors claiming her ex Derek Xiao cheated on her. Rehfuss, 29, took to X on Sunday, February 1, to share a screenshot of a fan comment that read, "Claire BB23 liking two of my TikToks that exposed Derek BB23 of cheating on her with his coworker Olivia and dating a week after they broke up." The screenshot was originally shared by an X user who captioned it with, "Derek from BB23 cheated on Claire. Whitney's karma." (During season 23 of Big Brother, which aired in 2021, fellow housemate Whitney Williams and Xiao, 28, clashed, with Williams claiming he was a huge threat on the series.) Rehfuss shared the post in full, writing atop the screenshot and caption, "This random f***ing account has been harassing us since we got off Big Brother. They've been racist, made up SA claims, threatened to kill my niece, harassed people I've followed etc." Big Brother's Derek Xiao and Claire Rehfuss' Relationship Timeline The reality star also stated, "Derek didn't cheat," before adding, "Don't engage with this pathetic stalker." Rehfuss announced via her Instagram Stories in September 2025 that she and Xiao, who also competed in The Amazing Race together in 2022 and won, had called it quits after four years of dating. "Hi everyone, after four wonderful years together, Derek and I have decided to end our relationship. Nothing dramatic happened, just the realization that we're different people who want different things," she wrote at the time. The AI engineer continued, "We still care deeply about each other [and] are grateful for the time we shared and will remain friends. Thank you for all the love and support, it truly means so much. We hope that by sharing, we can be given the space and grace to move forward without any speculation or drama." The announcement was signed by both herself and Xiao, and Rehfuss added a purple heart emoji. Xiao later shared the post via his own Instagram account. Amazing Race's Derek Xiao and Claire Rehfuss Return for Season 35 Premiere The former couple had met while filming the reality series before their friendship turned romantic after they were both eliminated and evolved into jury members. Rehfuss exclusively told Us Weekly after the series wrapped in October 2021 that she believed they "both really felt chemistry" after arriving in the show's jury house. "We would stay up late talking every single night and we just really developed a bond." Derek was also interviewed about the pair's relationship at the time, telling Us that he recalled "such a strong connection and chemistry" with Rehfuss. "I think that was the beginning of us thinking about what this could be. I knew from week one that Claire was my type. I guess I just never let myself explore that beyond just a friendship," he said. After the duo won season 34 of The Amazing Race, which saw them awarded $1 million in prize money, they moved in with one another in California. After they split, Rehfuss notably stepped back from the public eye, returning to Instagram in November 2025. Appearing happy in an apartment on her own, she captioned a November 11 video, "Took a little break from social media and ended up picking up a new hobby instead 👀 This was my first ever knitting project (because scarves are boring) and I can't believe how easy it was." A subsequent Instagram video, shared two weeks later, confirmed that she had moved into a "new apartment."