Karlie Kloss plays fifth wheel on double date with Taylor Swift and Calvin Harris and Gigi Hadid and Joe Jonas

You wouldn't expect a model as beautiful as Karlie Kloss, 22, to be the odd woman out…or the fifth wheel on a double date.

But there she was, pulling unofficial "tour guide" duty for budding couples Taylor Swift, 25, and Calvin Harris, 31, and Gigi Hadid, 20, and Joe Jonas, 25, in London.

Taylor posted a pic of the quintet on Instagram with this caption: "Little known fact. Karlie is secretly an unofficial historian/London tour guide. Kind of."

Was that Tay's sweet way of acknowledging her fifth-wheel status?

Gigi and Joe may have yet to officially come out as a couple, but their body language says everything they haven't. The pair also hung out with Kendall Jenner, Drake, Rita Ora and other young, rich and beautiful stars at the Libertine Club on Sunday night.

Ah, what a life! The party never ends for Hollywood's youth.

Gigi and Karlie previously joined Taylor onstage over the weekend for a Hyde Park performance of 'Style'. Watch the video below.