When: 1988-1989

Sin-who? Sinitta is an American-born singer who had a string of hits in the UK in the '80s and was an early protegé of Simon Cowell. She was also his on-again, off-again girlfriend for about 20 years, starting in 1984. 

Smash Probability: Established British pop star dates American quasi-nobody—you be the judge.