The duo — dating since 2003 — confirmed their split Thursday in a joint statement.
"We have, in fact, ended our romantic relationship, and have done so mutually and as friends, with continued love and respect for one another," the pair said.
The two said they usually prefer not to comment on their relationship, but recent speculation and inaccuracies prompted them to issue the statement.
Timberlake just launched his "FutureSex/LoveSounds" tour and his feature film, "Alpha Dog," is scheduled to open Friday. Diaz most recently appeared in the romantic comedy, "The Holiday," with Kate Winslet.