It's a big day for Tim Cook, too.

The Apple CEO surprised iPhone enthusiasts who were lined up outside an Apple store today in Palo Alto, California, waiting to buy the new iPhone 6 and iPhone 6 Plus.

Cook posed for selfies with Apple enthusiasts and cheered alongside them when it came time to open the doors at 8 a.m.

The phones, which were unveiled at a Sept. 9 media event in Cupertino, California, are already shaping up to be one of Apple's biggest successes to date. Pre-orders for the smartphones have broken all previous benchmarks, according to the tech giant.

Cook has called the plus-sized devices the best phones Apple has ever produced.

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