According to the gossip site Radar, the rapper changed some lyrics to a song to imply his wife is pregnant with a sibling for their two-year-old daughter Blue Ivy.
The website says Jay Z included the words 'cause she pregnant with another one' during the first of the couple's two shows in Paris.
Bey and Jay are currently on the European leg of their On The Run tour and as they sang the track Beach Is Better to a huge audience in Paris, Jay is said to have messed with the lyrics to make the surprise announcement.
There are no reports of any response or reaction from Beyoncé during or after the show.
OK, as rumours go, it perhaps isn't the most concrete we've ever come across, but it does beg the question why Jay, 44, would make the lyric switch?
Can it be true that Bey is pregnant again? Or was Jay was just being mischievous because he's fed up with the constant speculation that he and 33-year-old Beyoncé are on the brink of divorce?
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Or perhaps it was just all part of the show, because the story strung through the tour concert chronicles a couple - played by Bey and Jay - who are madly in love, endure problems, and then reunite after concluding that forgiveness is key.
The couple - who have been married for six years - already have one daughter, two-year-old Blue Ivy, who was born in January 2012.
OK! magazine suggested last week that there may have been pregnancy news on the horizon, with a source claiming that the rapper had been 'fiercely protective' of Beyoncé lately, 'just like he was when she was expecting Blue Ivy.'
The magazine's source added: "He's been doing everything he can to ensure that Bey is in a stress-free bubble.
"He's informed their entire entourage that they need to use relaxed voices, mellow lighting and listen to only soft music, and he's said that all of the food Beyoncé eats should be organic."
The couple looked very much in love last week on Beyoncé's birthday - September 6 – as they strolled through Portofino, Italy.