Twice F1 world champion Alonso signed a multi-year contract with Aston Martin on Monday, joining them as a replacement for German Sebastian Vettel (35), who last week announced his retirement from racing at the end of the current season.
Alonso's decision to join Aston Martin came as a surprise to Szafnauer, who was confident Renault-owned Alpine had been on the verge of signing the 41-year-old driver to a new contract.
"It was the first confirmation I had," Szafnauer told reporters on a Zoom call. "Obviously, when we're in the paddock, there's all sorts of rumours, and I had heard rumours that Aston were interested.
"Once you hear that they're interested, there's probably discussions that took place... But I was confident that, even with the discussions, and there's nothing wrong with exploring, that we were very close.
"So yes, the first confirmation I had was the press release. I did ask the question (to Alonso). And I was told: 'No, no, I haven't signed anything.' So I was a bit surprised."
Szafnauer said Alpine had offered Alonso a contract extension which would have guaranteed him a seat for the 2023 season with an option to extend for another year.
"We offered a one plus one deal. And we discussed with Fernando that: 'Look, if next year at this time you're performing at the same level, of course, we will take you and that could have carried on'," he added.
"But I think he wanted more certainty independent of performance: 'I want to stay for longer.' And I think that was the crux of the going one plus one as opposed to two plus one or three plus one or three years."
