I wasn't entirely sure this was true, but now that the AP has said that it isn't, I guess that it is

AP fact checks Queen Elizabeth death meme and concludes it is unlikely to be authentic

Related: Hillary Clinton has left England, and will not be returning for the Queen’s funeral: “My work here is done”, she told FWIW, before boarding her private jet at Heathrow, “and now it is time to let the poor, dear lady rest in peace.”