повезло, что никто не видел, как

was lucky that nobody saw how

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phrase Rare #51,074
was lucky that nobody saw how The person who was lucky is expressed in the dative case; the phrase can continue with what nobody saw them doing.
RU: Ему повезло, что никто не видел, как он потерял ключи.
EN: He was lucky that nobody saw how he lost his keys.