Jules Knight, who sings with classical fusion band Blake, attended St Andrews with the royal pair.
The Sun reports that Knight will play "dishy but arrogant" new doctor Harry Tressler in the hospital drama.
Knight, 31, revealed that he is eager to pursue an acting career, saying: "I can't wait to get stuck into Holby City, which is a programme I have always watched and admired.
"I feel incredibly lucky to have experienced six fantastic years with Blake, touring the world, recording and releasing albums, even winning a Brit - all with three great friends... I wish them all the very best with the release of the new album, Start Over."
Holby City's consultant series producer Justin Young said: "At first glance, Harry Tressler seems like a charming, arrogant public schoolboy that we'll love to hate, but there's much more to him. His arrival on the wards is going to really shake things up."
Watch Jules Knight perform with Blake on GMTV below: