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Year 100,000,000,000,000,000,000,000,000,000,000 AD, or 100 nonillion, was a year speculated to be the end of the universe itself. (PDA: The Infinity Doctors)

However, the end actually came much earlier, in year 100,000,000,000,000. The Tenth Doctor visited this time with Martha Jones. (DW: Utopia)