Sebastiaan Bornauw (born 22 March 1999) is a Belgian professional footballer who plays as a defender for 1. FC Köln in the Bundesliga.
Bornauw made his professional debut for Anderlecht in a 1–4 Belgian First Division A win over K.V. Kortrijk on 28 July 2018 at the age of 19 years old. He played the full game. Bornauw would go on to become a key defender for Anderlecht, despite his young age. In total, he played in 24 league games and he scored 1 goal as a defender for Anderlecht in his debut season.
1. FC Köln
On 6 August 2019, Bornauw joined 1. FC Köln on a five-year deal. He scored his first Bundesliga goal on 20 October 2019 against SC Paderborn. In his first season at 1. FC Köln, Bornauw established himself as a regular starter and became a key player for the club.