So, what was it? Another hat! Mike had a miniature version of his headwear stashed inside his hat, which he then returned to same place once his party trick had been delivered.
‘The Queen was definitely amused,’ says an onlooker.
Also present for the gag was Sophie, Countess of Wessex, who had front row seats to the performance.
Mike seemed to be having a great time with Bea, going in for a comedy kiss that almost had her eyes popping out of her head - and all under the gaze of her dad, Prince Andrew.
Prince William also got the treatment, with Mike sticking his tongue out in a decidedly unroyal moment that was captured on film.
Those unfortunate enough to be less close to the high spirited royal action – including TV watchers - were left guessing what was going on, and exactly what Mike had pulled out of his hat that was so funny.
‘It's those chocolates you can buy in the shop I think? Very funny,’ one viewer posted, wildly inaccurately.
‘It's a large Nespresso capsule,’ said a second, while a third suggested it was a yoghurt pot.
While Prince Harry and Meghan Markle were absent from Ascot, Mike and keen horsewoman Zara are regular attendees – and were clearly having the time of their lives at the horsey event. Perhaps that explains Mike's merry mood!