Leonard is the son of Adrian Degenhardt and the late Francesca von Lahnstein. He is also the brother of Constantin von Lahnstein and the half-brother of Carla von Lahnstein. Until 2007 he believed that Johannes von Lahnstein was his real father, but a letter from his late mother Francesca sheds another light on his paternity. A DNA test proves that Adrian is indeed his biological father. Leonard is the favorite son of his father Johannes. When he comes home from Chicago, where he worked as doctor, he meets the beautiful Cécile de Maron and knows from the beginning that she is the love of his life. He arrives at Königsbrunn and it turns out, that Cécile is Johannes's new wife. Soon, Leonard and Cécile have to deal with their feelings for each other. They try to deny their love, and Leonard even marries his former love Silke Voss to prove that he can live without Cécile. But his marriage falls apart when Silke sees that Leonard is in love with Cécile. Johannes also tries to come between Leonard and Cécile's love. When he finds out they had an affair, Johannes files for divorce and wants Leonard out of his life. Cécile tries to bring them back together when she finds out that she is pregnant and hopes that Johannes finds a way to be a grandfather to their child, but Johannes refuses. Just a few days after marrying Leonard, Cécile and her unborn son, Julius, die after a car accident. Johannes comes to Leonard and comforts him when he needs him most. Leonard soon becomes addicted to pain killers and is haunted by memories of Cécile. His family and friends try to help him and he finally sees that it's worth living again. Then he meets the new maid Sarah Hofmann and falls in love with her. Their relationship doesn't last long since Sarah discovers that she is the product of a one-night stand between Elke Käppler and Johannes, making Leonard and Sarah half siblings. Sarah and Leonard break up and try to move on. Leonard begins a passionate affair with his good friend, Jana Brandner, while Sarah begins to fall for Gregor Mann. But Leonard and Sarah can't stop thinking about each other. Still, Sarah marries Gregor and Leonard marries Jana. However, just a couple of hours after marrying Jana, Leonard finds out that Adrian Degenhardt is his biological father, meaning him and Sarah aren't related after all. Since they are already married, they both to decide to honor their vows and stay with their spouses. Eventually, Sarah and Leonard give in to their feelings and have a one-night stand, which Leonard immediately regrets. Sarah realizes she wants to be with Leonard, but then finds out she is pregnant with Gregor's baby. Jana finds out about their one-night-stand. She decides to forgive both of them and agrees not to tell Gregor. Jana and Leonard decide to make a fresh start and decide to move to Chicago. On the day of their living party, Jana overhears Sarah begging Leonard to stay. Jana confronts Sarah, who is apologetic, but doesn't deny her feelings for Leonard. Jana and Sarah get in a car together and later have a crash. Sarah is seriously injured and requires surgery. Sarah loses her baby and Gregor blames Jana, who is guilt-ridden. Jana tells Leonard that she is now willing to let him go to be with Sarah, realizing that he'll never love her like he loves Sarah. Jana has a pulmonary embolism and isn't given long to live. She tells Sarah and Leonard that they are perfect for each other and reunites them right before she dies. Leonard, Sarah, and all of Jana's loved ones are heartbroken over her death. When it is revealed that Leonard and Sarah slept together, everybody blames them for her death. Gregor leaves Sarah and declares he wants nothing to do with her or Leonard. Eventually, Leonard and Sarah manage to find their way back to each other and gain forgiveness for their mistakes. They finally get married in Königsbrunn with their family and friends present. In May 2009, Sarah moves to Boston to go to music school. In September 2009, Leonard also moves to Boston to be with his wife.
