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.
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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.
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