The Wizarding World keeps expanding and changing, so you never know what kinds of additions J.K. Rowling will create to make this magical universe even more complete. We already have the Fantastic Beasts franchise which already made some changes to canon, but new details appear on Pottermore all the time.
Nevertheless, the world of Harry Potter is crazy enough already to have the most surprising relatives you could possibly think of, so here are ten characters you didn't realize Harry was related to.
10 Dudley Dursley
The most obvious one is definitely Dudley Dursley. Despite Harry living with the Dursleys since he was only one year old, the fact that he is related to them is not focused on that much. In fact, the hatred between Harry and the Dursleys is probably the reason why you could easily forget about his relationship with them.
Dudley's mother Petunia is the sister of Harry's mother Lily Evans. This makes Petunia and Vernon Dursley Harry's aunt and uncle while Dudley is his cousin. It's amazing how different Lily and Petunia are and the kinds of families they created.
9 Victoire, Dominique, Louis
Victoire, Dominque, and Louis are the three children Bill Weasley and Fleur Delacour had, and believe it or not, Harry is actually related to them. This connection can be traced through the Weasley bloodline and then through the Black bloodline (Harry's connection to the Black family will be explained later on).
Bill is the eldest son of Arthur and Molly Weasley, both of whom can be traced back to Harry's ancestors. Arthur is the son of Septimus Weasley and Cedrella Black. Cedrella's grandparents are Urula Flint and Phineas Nigellus Black who also happen to be Molly's great-great-grandparents on her mother's side. Because of Harry's marriage to Ginny, he is also somewhat related to all these people.
8 Rose Weasley
Because of Harry's connection to the Weasley family, it is only logical that he would also be related to his best friends' daughter Rose. Her parents are Ron Weasley and Hermione Granger (which kind of resembles the situation with Harry's parents where both Hermione and Lily are muggle-born, while their husbands are purebloods).
Harry is Rose's uncle because of his marriage to Ginny who is Ron's sister. In addition to that, they are very distant relatives through the Weasley and then the Black bloodline.
7 Scorpius Malfoy
Because of Harry's relationship with the Black family, he is also related to Draco Malfoy and his son Scorpius. Draco's mother is Narcissa Lestrange whose birth name was Narcissa Black. Her bloodline goes back to Urula Flint and Phineas Nigellus Black who, as mentioned earlier, are related to the Weasleys.
Now, because of Harry's relationship to the Weasleys in the form of his marriage to Ginny, he is also indirectly related to the Malfoys. It's kind of a tight one, but it's still an interesting connection.
6 Teddy Lupin
You could say that Teddy Lupin is connected to Harry through his marriage to Victoire Weasley (Bill and Fleur's daughter), but there is another connection through Teddy's bloodline.
Teddy's parents are Remus Lupin and Nymphadora Tonks. Nymphadora's aunt is Narcissa Malfoy because Nymphadora's mother is Andromeda Black, Narcissa's sister. This way, you can trace the bloodline the same way we did with Narcissa.
5 Sirius Black
Narcissa Malfoy is related to Sirius Black and both of them are, in turn, related to Harry himself. Sirius's parents are Orion Black and Walburga Black. Walburga had two brothers: Alphard and Cygnus.
Cygnus Black Druella Rosier had three daughters: Bellatrix, Narcissa, and Andromeda. This way, Harry also happens to be related to Bellatrix Lestrange.
4 Regulus Black
This one is pretty simple. Regulus Black is Sirius's brother. You might have forgotten about him a little because of his seemingly insignificant role in the story, but he was actually very important.
Regulus was a Death Eater who realized that Voldemort was going to use any means it takes him to conquer the world and that would mean killing many people. This is why Regulus turned his back on the Dark Lord and hid one of the Horcruxes, so Voldemort couldn't find it.
3 The Peverell Brothers
A lot of information about the three Peverell brothers has been lost, but their more recent heirs are still known. The Peverells played an integral role in the entirety of the Harry Potter series as they were the ones who got the Deathly Hallows that many wizards were later looking for.
Harry's father James Potter happened to be a descendant of the youngest brother Ignotus Peverell who got the Cloak of Invisibility from Death. The cloak is a relic that has been passed down from father to son ever since Ignotus started the tradition, so Harry got the cloak from Dumbledore who kept it after James had died.
Just like James Potter is the descendant of Ignotus Peverell, Voldemort is actually a descendant of Cadmus Peverell, the middle brother who owned the Resurrection Stone. Once again, a lot of information was lost, but there are still some things we know.
Voldemort's real name is Tom Marvolo Riddle Jr. His parents were Tom Riddle Sr. and Merope Gaunt (their story was quite tragic which is probably one of the reasons why Tom became Voldemort). Merope's father was Marvolo Gaunt who was a direct descendant of Cadmus Peverell and had the stone that was then taken by Voldemort and turned into a Horcrux.
Another character from Harry Potter and the Cursed Child is Delphini who turned out to be the villain of the story all along. The latest addition to the Harry Potter series might not have been liked by most fans, but it was still admired by some readers. In any case, it does change the canon a little.
Delphini is Voldemort and Bellatrix's daughter who was conceived and born sometime after Bellatrix was freed from Azkaban and before the final Battle of Hogwarts. Through her father, she is related to the Peverells which makes her related to Harry. Through her mother, she is related to the Blacks who are also connected to Harry.