No, it wasn't Pharrell or Justin Timberlake - the creator of the McDonald's 'I'm Lovin' It' jingle was in fact Pusha T.

The revelation was made by former music executive/current marketing CEO Steve Stoute (who cut the deal) during an interview with Hot 97; you can watch that below (he talks about it around the 4-minute mark).

And in case you'd forgotten what it sounds like (as if you could), here it is too: