Ray Jennings, a former South Africa international wicketkeeper, only saw his son had made a ton against India when his power returned an hour later.
"When he reached 96 the electricity went off, so I missed his hundred," he told BBC Radio Newcastle.
"When it went back on an hour later, I watched one ball and then he got out."
Durham left-hander Keaton, whose mother was born in Sunderland, became eligible to play for England in 2016 after serving a four-year qualification period.
The 24-year-old opener top-scored with 112 as England ended day one on 288-5 in the fourth Test against India.
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Asked what he said when the power went off, Jennings Snr said: "I'm sure a lot of your listeners would know it wouldn't have been a long sentence - it would've been short and abrupt, but I wouldn't be able to repeat it on air.
"It was a little bit of a bitter ending, but I'm very happy to know he actually ended up getting a hundred.
"Keaton keeps on telling me that one of the things I've done well is marry a British lady, so she's [his mum] over the moon and Keaton's over the moon.
"I've suddenly moved away from supporting a South African side to supporting an English side, and I'm very proud to actually say that.
"It's probably the most enjoyable sporting day I've ever had - for someone in your own family to achieve something like that has really been a blessing for me."

Wicketkeeper/batsman Billings is one of eight England players at IPL 2017, double the number who played last year.
"It gives you another platform to progress as a cricketer," the 25-year-old told BBC Radio Kent.
"My game's gone from strength to strength, playing international cricket around the world."
Billings played five games for the Delhi Daredevils in last year's IPL and has been retained for this year's tournament, which runs from 5 April to 21 May.
Every franchise this year includes an English player, with Eoin Morgan, Ben Stokes, Jason Roy, Jos Buttler, Chris Jordan, Chris Woakes and Tymal Mills also taking part.
Billings has also played in the Big Bash, for Sydney Sixers, and the Pakistan Super League, for Islamabad United, and feels the perception of English cricketers is changing as a result.
"Ten years ago, if you said an Englishman would go over and play in an Australian team, people would laugh at you," he said.
"I think we had 10 former or current English internationals playing in that, so we've definitely been put on the map.
"I'm really excited for the IPL. It's a fantastic competition, one of the best in the world.
"To have 60,000 people screaming at you and abusing you is a different concept, but it's an amazing experience.
"It's re-energised the game and given it a boost. It's just great fun."
Keaton Jennings' dad Ray says he missed his son's England debut century because of a power cut while he was watching the Test on television in Mauritius.
[NEXT_CONCEPT]
Kent's Sam Billings believes experience of tournaments such as the Indian Premier League and Australia's Big Bash can only improve English cricketers.