Two social tennis players got the surprise of their life in San Francisco on Sunday, when women's world number one Serena Williams interrupted her late-night stroll to challenge them to a hit.
The 23-time grand slam singles champion, fresh from her latest major triumph at the Australian Open last month, was out walking her dog Chip with fiance Alexis Ohanian when she passed two men trying their hand at the sport that has made her a global icon.
"Just having a stroll at night and I'm thinking about asking these guys if I can hit - just to see their reaction," she said in a video recorded by Ohanian and posted to Snapchat.
"I think they're in the middle of playing out a point. I'm going to ask if I can have the winner. I think I heard them say my name already - dang it," she added, her ruse having been quickly rumbled.
The 35-year-old American was not ideally equipped for the occasion, with a pair of soft, calf-high boots unlikely to be her footwear of choice on the WTA circuit.
"I don't have on my Nikes, but these'll work," she said.
"I'm not going to warm up!"
There was even time for some light-hearted trash-talking, as her star-struck opponent planted a forehand rally ball into the net.
"Don't get tight," she jokingly said.
Williams herself summed things up at the end of the encounter, sending out a message that will have amateur tennis players all over the world keeping a careful eye out for any mystery spectators.
"The moral of the story is, you never know when I'm going to be coming to a tennis court near you," she said.