Constantin von Lahnstein is a fictional character on German soap opera Verbotene Liebe (Forbidden Love) and was portrayed by actor Milan Marcus. He made his first appearance on 9 December 2004. The character was introduced as the last original member of the Lahnstein family as a troublesome teenager that grow up at his aunt's in Italy after his mother died. He has been featured in numerous storylines, including finding his biological father, his friendship to Paul Brandner, his relationships to Paul's sister Lisa and Judith Hagendorf and an affair with the former wife of his cousin, Nathalie Käppler. Marcus decided to focus on college in 2008 but stayed with the show until his last appearance on 5 January 2011.