According to the source "Mirrors" is his 4th #1. He's not credited for "Where's The Love".
Mirrors is the ex-*NSyncer’s second solo Number 1 in the UK as a lead artist, and
his fourth overall including hit collaborations 4 Minutes (with Madonna) and 2007’s Give It To Me (with Timbaland and Nelly Furtado). Mirrors is taken from Timberlake’s forthcoming third album, The 20/20 Experience, which is due for release later this month.
Congrats anyways, Mirrors is amazing