Alfred: "Sir! You've become even younger! Why, you don't look much older than Master Dick, and he's been Nightwing for years now!
Bruce: "Another Lazarus Pit bath after a fall into toxic waste, courtesy of Talia. Then, our passion got the better of us."
Alfred: "Gasp! You actually slept with her, sir?"
Bruce: "I'm sure it'll produce nothing negative. You know the drill?"
Alfred: "Like clockwork, sir. Another face lift it is, then..."
Especially because of the Nightwing comparison and the "Gasp!" followed by Alfred's "You actually slept with her, sir?" So much more sensible than certain other theories.