Little mistake

Our son (10) in an utmost sentimental tone):
‘Papa, you are my 2nd best papa in the world!!!!’
My husband (in his sober-minded self):
‘My dearest son, under no circumstances would I intend to interrupt you…but who is the 1st one?’
Walter (after a short pause):
‘I mean the 1st one. 
Sorry, little mistake in my calculations.’