Avid readers of Warren Buffett's annual investor letter complained over the weekend that the legendary investor's 2019 missive was a little repetitive, as Buffett once again lamented that Berkshire didn't see many options for investing its $100 billion cash pile - despite his desire to make another big deal. After accruing just $4 billion in GAAP profits for the full year, analysts and the WSJ described 2018 as one of Buffett's "worst years ever", as an unexpected $3 billion writedown on its investment in Kraft Heinz during Q4 helped lead to a $25 billion loss on the quarter.

But as Buffett revealed during an interview Monday morning on CNBC's Squawk Box, it nearly wasn't so. Because while Berkshire Hathaway didn't pull the trigger on any new deals last year, it did come close to pulling the trigger during Q4. However, the deal ultimately fell through, and Buffett said he didn't think it was "still on the books."

"We had at least one deal possible that would have been very large," Buffett told CNBC's Becky Quick from Berkshire-owned Nebraska Furniture Mart on Monday. "I liked stocks in the fourth quarter but I would like buying a business even better."

In his letter, Buffett explained that, while the prospect of buying a company makes he and Berkshire No. 2 Charlie Munger's "pulse rates soar", the sky high valuations for any companies with decent long-term prospects meant that Berkshire would likely continue to focus on buying marketable securities in 2019.

"That disappointing reality means that 2019 will likely see us again expanding our holdings of marketable equities. We continue, nevertheless, to hope for an elephant-sized acquisition. Even at our ages of 88 and 95 – I'm the young one – that prospect is what causes my heart and Charlie's to beat faster," he said.

When asked for a hint about the mystery deal, Buffett said only that the company he had in mind was "on this planet." Berkshire hasn't bought a company since 2015, when it bought Precision Castparts in a deal valued at $32 billion.

Watch a clip from the interview below:

Warren Buffett says he was close to making 'very large' acquisition in Q4 but it fell apart from CNBC.