Shawn Mendes brought out Niall Horan at his show in London for a surprise duet of "This Town." "I'll remember this for a long ...

Shawn Mendes invited former One Direction singer Niall Horan to join him for a surprise duet of Horan's debut solo single ...

If the whole world were watching, Niall Horan and Shawn Mendes would still make surprise appearances at each other's concerts ...