Severus shows up twenty minutes before the wedding. He probably has orders to kill her, but Lily ignores good sense and lets him into the boudoir anyway.

He gives her a compliment: "You look beautiful."

A rebuke: "I always thought you could be more than James Potter's little wife."

A wedding present: "There are plans to attack the Hogwarts Express, but at the Hogsmeade end, not King's Cross."

He tells her he will always love her, kisses her (on the lips!), and leaves.

She walks down the aisle with a smile on her face and a song in her heart, but one small refrain croons regret.