You may be searching for the father of Karl-Franz: the late Emperor Luitpold.
Prince Luitpold is the eldest son and heir-apparent of Emperor Karl Franz. It's widely expected that, upon his father's death, Luitpold will be elected as new Emperor, provided he doesn't antagonize the Electors.
Notes & sources
- Warhammer Companion states that Drachenfels was defeated by Oswald in 2480 IC and the theatre-play is performed 25 years later when Luitpold is 12 years old. Ergo: 2480 + 25 - 12 = 2493. However the timeline appearing in the Boxtree books states that Luitpold was born in 2491. The Boxtree timeline also states that Karl Franz was elected and crowned in 2491.
- Drachenfels (novel) written by Jack Yeovil (aka Kim Newman)