Becker, 41, and his partner, Dutch model Lilly Kerssenberg, were guests on the German show You Bet?, which was being watched by 9.7 million viewers when the surprise announcement came. According to Reuters, presenter Thomas Gottschalk looked astonished and said: "No, not again?"
Becker and Kerssenberg split at the end of 2007 after dating for two years. The tennis ace then became engaged to jewellery designer Sandy Meyer-Woelden after seeing her for only a few months.
That relationship ended in November 2008 and Becker later confirmed that being dumped by text message had "trampled on his soul".
Becker said on the show that his wedding to Kerssenberg will take place in June at the resort of St. Moritz, Switzerland. "Last summer I went a bit off track but she took me back. Now I don't want to let her go," he added.