With Adyelya's birth, Klaus and Katherine are the only two characters, so far, to become parents during the series. Klaus and Katherine conceived their daughter during a drunken one-night stand, when they hated and were hostile with each other.
Throughout The Vampire Diaries
In the season four finale of The Vampire Diaries, Graduation, Katherine slept with Niklaus Mikaelson and conceived her daughter, Adyelya.
Katherine was the next doppelgänger after Tatia; a woman whom Klaus was in love with and who was identical to Katherine. Klaus eventually develops feelings for Katherine in The Originals.
The family relationship between Klaus Mikaelson, Hayley Marshall-Kenner and their daughter, Hope. Klaus and Hayley conceived her in Mystic Falls after that Klaus saved Hayley from Will. They dealt with Hayley's pregnancy with Hope and the fact of becoming parents during the first season of The Originals.
In death, as in life, Katherine Pierce is as selfish as she was over the last five centuries. Just after her daughter, Nadia, dies of a were-bite, Katherine finally can't outrun her enemies. Stefan plunges the Traveler's knife into Elena's body, expelling Katherine's spirit.
Who are Klaus Mikaelson's offspring? Klaus has two known progeny – Hope and Hayley Marshall-Kenner.
Katherine gave birth to Nadia back in 1490, but Nadia was taken from her before Katherine even got the chance to hold her. When Katherine returned to Bulgaria after being exiled to England and escaping Niklaus Mikaelson, she found that he killed her entire family and was devastated.
Season Four. The Original Hybrid, Klaus Mikaelson, and the second-known Petrova Doppelgänger and newly-turned human/witch of the Traveler sub-culture, Katherine Pierce, slept together in Graduation and conceived their daughter, Adyelya.
As a result of her unique heritage, she is the world's first werewolf-witch-vampire hybrid. She inherited her werewolf gene from both of her parents, while her vampire and witch legacy came from her father who is the Original vampire-werewolf hybrid and the son of the Original Witch.
Literally the explanation is that Klaus was born a werewolf, so he can procreate. Every hybrid on the planet was born a werewolf. The CANON ANSWER is that he triggered the curse thus he can procreate.
Stefan Salvatore is objectively Katherine's best love interest in the series. He was the only person that she loved unconditionally, and it was Stefan that made viewers see Katherine as less of a villain and more of an anti-hero.
The Curse of the Sun and the Moon was bound with Petrova blood. And the Petrova doppelganger was created to undo the spell. Thus, Klaus needed Katherine to drain her blood as a sacrifice to break the spell.
Katherine Pierce (born Katerina Petrova) was one of the main characters from The Vampire Diaries and eventually became a major supporting character in the second season and third season of The Originals Fanfiction and the first two seasons of Eternal Darkness. She later became a main character in the third season.
“Yes, I slept with Klaus, but after you walked away from me,” she reminded him. “Get over it or get out of my life.
In 1490, when she was about 16 or 17 years of age, Katerina became pregnant by an unknown man, a Traveler, and her family disowned her for the shameful birth of an illegitimate daughter.
Nadia was Katherine's only child. Katherine gave birth to Nadia onscreen, though these were in flashbacks in the episodes Katerina and 500 Years of Solitude.
Henrik is the tribrid son of Niklaus Mikaelson and Hayley Marshall-Kenner. He is the twin brother of Hope Mikaelson and the paternal older half-brother of Octavia and Remus Mikaelson.
This was a predicament Klaus Mikaelson, Hope's father and first supernatural hybrid, struggled with in his quest to create more vampire-werewolf hybrids. However, Hope is the only vampire-werewolf-witch tribrid that Nature has ever allowed to exist.
He was forced to send her away to live with her aunt Rebekah to protect her from those who would try to harm her, or those who would target her for being a Mikaelson.
Eventually, Katherine accepts that She is Deeply in Love with Klaus and and Elijah, and is unable to live without Either by her Side; Klaus and Elijah come to Understand that they also both love Katherine too much to leave her, They All agree to enter a Polyamorous Relationship.
Can Hybrids Have Babies? Mules and bananas are examples of hybrids that are infertile, so they cannot have their own babies. But surprisingly, there are many examples of hybrids that actually can have babies. This happens when the hybrid mates with another hybrid, or with the same species as one of its parents.
He reveals himself to Katherine in Know Thy Enemy. In The Last Dance, Klaus—who still was in Alaric's body—gets information on Elena and her friends. He then compels Katherine to hurt herself by sticking a knife in her leg and repeating it again and again.
It is revealed that Elena is a Petrova Doppelgänger (like Katherine, Amara and Tatia), which is thus responsible for her being identical to her ancestor, Katherine Pierce (née Katerina Petrova). This also has the implication of making her a supernatural creature.
That bloodline eventually lead to the Flemming family (Elena's birth mother). Isobel Flemming gave birth to Elena. So, Katherina is Elena's ancestor. Katherine is like her great great great great grandmother.
The two of them discuss what happened between Stefan and "Elena" and Caroline also tells him about Nadia and Matt and the text he sent to her. From Matt's text, who used "K" and not "E", they put the pieces together and they realize that Katherine is in Elena's body.