The major twist of Big Brother 4 (US) was the X-Factor. Eight houseguests were introduced, only to have five houseguests exes compete against them in the game. This resulted in the game quickly became messy, as Scott Weintraub, a houseguest who had his ex-girlfriend Amanda Craig move into the house, had a violent outburst, and subsequently told the House that he had a sexually transmitted disease. He was expelled from the game. The ex-couples were:

The twist would later reappear during Big Brother 8 (US), coinciding with the Rivals twist, where Joe Barber entered the house and then discovered that his ex-boyfriend, Dustin Erikstrup, was also going to be playing the game.

The twist reappeared again on the following season, Big Brother 9 (US), with houseguests Sharon Obermueller and Jacob Heald being exes playing the game together. This twist coincided with the Soulmates twist, and the two were paired up together. However, their time in the game was cut short, as they were evicted by the Power Couple on Day 3.

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