If anyone looked out of their window now, even beady-eyed Mrs. Dursley, they wouldn’t be able to see anything that was happening down on the pavement. Dumbledore slipped the Put-Outer back inside his cloak and set off down the street toward number four, where he sat down on the wall next to the cat. He didn’t look at it, but after a moment he spoke to it.
“Fancy seeing you here, Professor McGonagall.”
He turned to smile at the tabby, but it had gone. Instead he was smiling at a rather severe-looking woman who was wearing square glasses exactly the shape of the markings the cat had had around its eyes. She, too, was wearing a cloak, an emerald one. Her black hair was drawn into a tight bun. She looked distinctly ruffled. (Harry Potter and the Sorcerer's Stone)
What does the word ‘fancy’ mean, used when meeting someone you know on a place you’ve not expected? I don’t find any right meaning in OALD or Merriam-Webster’s.