Cassie and her twin brother Rex landed in Salem with the meteor shower in July of 2002, they were half-naked, spoke no English, and were originally believed to be aliens. It's now known that Cassie and Rex are human, and they have learned to speak, and have enrolled at Salem University with their friends Belle and Shawn.

After they had been in Salem for a few months, genetic testing revealed that they were really the twin children of Tony and Marlena (conceived through scientific means). Rex dealt fairly well with the news, his superior intellect making him a must-have for the local professors. Rex soon started dating Mimi, and she was by his side when he learned the awful truth...not only were Tony and Marlena not their parents, but his father was Roman Brady, a man that he despised, and his mother was Kate Roberts. The moment he found that out, Rex had to rush to find Cassie, because Cassie and Lucas were in bed together...and he had to tell Cassie that she was trying to seduce their half-brother!

Shortly after learning about their true paternity, Rex's attitude soon changed. He became moody and withdrawn, having headaches that worried his friends. He also became violent. When people started dying in Salem, Rex was the prime suspect. And when Maggie Horton's blood was found on Rex's sweatshirt, he was arrested and sent to jail. He was released in time for the Salem Fall Celebration, and as he held his twin's dead body in his arms, he cast the blame for her murder directly on Kate Roberts.

Rex never quite got the chance to know Roman Brady. Just as he was starting to, Roman was murdered at his own wedding reception. Rex was touched when his grandfather, Shawn Brady, turned to him for support. Not long after, Tony was murdered, and Rex cast off the last of his DiMera life and changed his last name to Brady.