Songfacts®:

• Here, Maisie Peters imagines throwing a Halloween party for 40 friends. Vancouver-born Cate Canning turns up with her brother, who's come over from Canada for a visit. Maisie immediately falls in love with Cate's brother, and after an initial hesitation she embarks on a full-scale romance.
• Maisie really has a Canadian friend named Cate, whose brother she met, but the rest of the narrative is a made-up story penned by Peters and Fat Max Gsus in Stockholm, Sweden. "Cate does have a brother, who is a sweet, sweet Canadian prince. No, we are not dating," she told People. "The song was literally just a joke for me and my friendship group. I wrote it in Sweden and was like, 'Oh, this will be funny.' And then lo and behold, out it came."
• That's when I became his only girl
  And now I date Cate's brother
  
  The song has a happy ending, but it nearly ended up with something sassier. According to Peters, for 15 minutes the last line was "and now I hate Cate's brother." Then she and Gsus opted for something more lighthearted.
• Joe Rubel supplied the sinewy pop-rock production. An Ed Sheeran cohort, Rubel co-produced his Equals tracks "Tides," "Stop The Rain," and "Love In Slow Motion" (Peters is signed to Sheeran's Gingerbread Man Records).
• Peters originally leaked snippets of "Cate's Brother" on TikTok, only for it to go viral. After her fans demanded its release, she dropped it as a single on May 6, 2022.
• So does Cate's brother know about the song? "I really did that as a surprise moment thing and it's really turned into something much bigger," she told Spin1038. "Ehm... Does Cate's brother know... Well, I mean he clearly knows now!"
• Maisie Peters released a new duet version featuring Matt Maltese on June 1, 2022. On "Cate's Brother (Matt's Version)," Maltese sings from the perspective of Cate Canning's brother.