Most astronauts "grow" during protracted space missions because their spines extend in the absence of gravity, but the gains are usually limited to a couple of centimeters (inches) maximum and disappear once they are back on the ground.
The 41-year-old Kanai, who went to space last month for a nearly six-month mission, posted on Twitter on Monday that he had "a big announcement."
"My height's been measured here in space and somehow, somehow, I've grown 9 cm! In only three weeks I've really shot up, something I haven't seen since high school," he tweeted.
"This makes me a little worried that I might not be able to fit in the Soyuz seats for our return."
But a bit over a day later - and in the wake of a flurry of news stories - he apologised, saying that he'd measured himself after his captain raised questions about the apparent growth and he had stretched only 2 cm from his Earth-bound height.
"This mis-measurement appears to have become a big deal, so I must apologise for this terrible fake news," he tweeted, without explaining how the original miscalculation had occurred.
"It appears I can fit on the Soyuz, so I'm relieved."
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(Reporting by Elaine Lies; Editing by Michael Perry)© Thomson Reuters 2018
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