Clue: A poor end to perform­ance after classy Here Comes the Sun? (6)
Answer: AUBADE
Explanation: Definition: Here Comes the Sun?
A charade of 'a' plus U ('classy') plus BAD ('poor') plus E ('end to performanc**E**'). A serenade is an evening song, and an AUBADE, one for the dawn, such as George Harrison's example ('?').