The real parts are that Gyles Brandreth, a friend of Prince Harry and Meghan Markle, has criticized them for their recent actions, and that the Queen is currently ill. The fabricated parts are that the Queen has been poisoned, that Harry and Meghan are responsible, and that Brandreth has called them "cruel liars."
There is no evidence to support the claims that the Queen has been poisoned or that Harry and Meghan are responsible. These claims are likely based on the fact that the Queen has been hospitalized recently, but there is no indication that her illness is anything more than a cold or the flu.
Brandreth has indeed criticized Harry and Meghan for their recent actions, but he has not called them "cruel liars." He has said that he is disappointed in their decision to step back from royal duties and that he believes they have caused a great deal of pain to the Queen.
It is important to be critical of the information you consume, especially when it comes to news about the royal family. There is a lot of misinformation out there, and it is easy to be misled. If you see a headline that seems too good to be true, it probably is.