Katie Hannaford, 34, was mortified after she flashed students, parents and teachers cheering from the sidelines.
Watch the video above to see the clumsy flash
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Hannaford was participating in her eight-year-old daughter’s parents’ race at her school sports day, after her daughter begged her to participate.
She told Britain’s SWNS news that she knew she’d come last, but got more than she bargained for in the end.
After losing her footing, she fell to her knees, and her dress flew over her head revealing her G-string.
She flashed onlooking students, parents and teachers crowded on the sidelines.
One adult directly behind Hannaford at the time can be seen covering her face in disbelief as the stumble turned into an accidental mooning.
Hannaford was initially mortified by the incident but has now come to see the funny side of it.
“Lessons learnt … I’m no longer 21 and shouldn’t run in the mums’ race and don’t ever wear a dress when running!” Hannaford wrote in a Facebook post.
“When the kids got more at sports day than they were expecting! Haha
“If you can’t laugh at yourself then what’s life about, ay? Sorry, kiddos, and anyone else watching!”
She told SWNS: “I just tripped over my own feet – I think my body was just moving too fast for my legs! I’m so clumsy, I’m always falling over.
“I was humiliated at the time, but it is what it is! I flashed my underwear, which is obviously embarrassing but you just have to own it.
“Looking back, it’s hilarious – definitely the funniest thing I’ve ever done in my life!”
Hannaford’s daughter had more luck in her own race, coming in first place.
The video was shared online and instantly went viral with many people commenting on Hannaford’s Facebook post with humour and support.
“10 points for the faceplant and 100 for the sense of humour,” one user wrote.
“This will go down as the most funniest sports day performance ever,” another wrote
“I’m actually in tears, imagine this was a granny knicker day,” another wrote.
“You need to laugh at yourself every so often as otherwise life is too serious. Nice to find another accident-proner. Thanks for the chuckle,” another wrote.