JAN Koum certainly had good reason to celebrate as WhatsApp turns five.

And it was perhaps appropriate that WhatsApp boss Jan Koum should be having a big night out with one of the world’s richest techies Mark Zuckerberg.

The pair were spotted partying at restaurant Boujis in Barcelona just days after it was announced that Zuckerberg’s company Facebook had bought WhatsApp for $19 billion.

They were photographed hanging out with Korean singer Psy after spending the day at the Mobile World Congress conference.

The free messaging service, which has a 96% penetration rate in Spain, turned five on the same day.