Many fans commented on the royals hat following Saturday's graduation ceremony.
Beatrice first made headlines in 2011 following the wedding of Prince William and Kate Middleton after donning a bizarre fascinator.
Beatrice's appearance at Sandhurst on Saturday comes after it recently emerged that she is dating multi-billionaire property tycoon Edoardo Mapelli Mozzi.
Friends have said things are going so well for the couple they could be tying the knot as soon as next year.
Beatrice has already introduced her new beau to her parents Sarah Ferguson and Prince Andrew, according to Express.
Mr Mozzi is a divorcee with a two-year-old son.