No, Udo Jürgens is an Austrian "Schlager" singer who has been around since the 60s (winning the Eurovision contest in 1966 so Mama might remember him) still being especially popular with the older ladies these days.
http://en.wikipedia.org/wiki/Udo_J%C3%BCrgens The musical is so-so, it is extremely cheesy. I like Mamma Mia, but this musical is even too much for me.
The story is so silly, written by the German novelist Hera Lind telling the story of the TV presenter Lisa whose mother runs away going on a cruise to New York with her lover she met in a nursing home to get married in New York.
Lisa (and her best gay friend, a hair dresser) and the son of the her mother's lover (and his son) follow them and they all meet on the cruise ship. The end of it is, of course, predicable.