Possible Clues:

• "Surprised to see you!"
• 'Fancy running into you here!'
• Surprised greeting
• "Whoa, didn't expect to see you here"
• 'Surprising to run into you here!'
• 'Fancy seeing you here!'
• "Fancy seeing you here!"
• "Just noticed you there!"
• 'I didn't see you there!'
• Informal greeting