They all look like each other though, that's the problem with these "person X looks like Y, so they must be their illegitimate child!"
Bea looks a bit like queen Vic, Eug has resemblance to Liz queen mum, Anne's son Peter and Will could pass for twins, Harry's looks take strongly after the Spencer side as well as queen Mary. Charles, Anne, Zara and Liz also take a lot after queen Mary (close set eyes, nose, lips, shape of face; Margaret and her daughter Sarah as well).
Diana has a good resemblance to the Goldsmith family (Jemima and her siblings), but when you look up earl Spencer's pics when he was young, he looks like Diana in drag. Same for her brother, Charles. One of Diana's nieces via one of her sisters looks like the spit of Diana (so much for the rumours that Diana is a Goldsmith spawn). Diana and her sisters look alike depending on angle and light, sometimes like 3 strangers, sometimes clearly relatives.
Will looks a lot like Diana, but there's the resemblance between Peter and Will (seriously, twins separated).
Little Charlotte looks like the spit of Pippa and Carole, but has quite a resemblance to Sarah Chatto. When you squint you might see a bit of Will. Never get anyone who says she looks like Liz. She doesn't.
George is all Mike, and Louis is also all Mike/James/Kate.
I can somewhat fancy to believe that Liz had a thing with Porchy, but not that Andy is Porchy's son.
Some of these people aren't even related and look like straight out siblings. I know also people who are very clearly from the same parents, yet they look nothing at all alike. They just take strongly after certain ancestors.
I guess all these people have some common anestors somewhere who peeks through (eg Diana, the Goldsmiths, Peter Phillips or Will and Porchy).
Fact is, we are all related after all, proven by maths and genetics!
The only question is, how far apart?