Marceli's father, Mikołaj Zielinski, was a muggle-born wizard who attended Beauxbatons. Marceli's mother, Anastasie Bellerose (b. Hélène Anastasie Bellerose), was a pure-blood witch from France. Anastasie had rejected a marriage proposal by another man, since she was dating someone else at the time. As an act of revenge, the rejected man kidnapped her and beat her, before dropping her off in Poland, knowing that she didn't know a single word of Polish.
Luckily, a former classmate of hers, Mikołaj, was walking home a different route his home. They had never really talked, they had been partners in a project, but other than that, they had no contact with each other.
Mikołaj had recognized her, bloodied and bruised by the side of the road, and took her home, to treat her wounds, as he knew French. During the next six months, they grew closer, and Anastasie learned Polish in secret, wanting to impress Mikołaj.
After nearly nine months in his home, they finally confessed their love to each other. They dated for a little for than a year, and two years after they met again, they got married.
Three years after they married, on a cold February day, their first child, or should I say, their first two children, were born. The girl, Helena Anastazja, was born two minutes before her twin, a boy named Marceli Aleksander, joined their family.
Mikołaj and Anastasie raised their family in Mikołaj's hometown of Kraków. They visited France, but never Anastasie's family, since they had encouraged her to marry the man that left her in Poland, for money. Mikołaj worked as a Muggle doctor, and Anastasie stayed at home, with the twins.
Marceli and Helena, known as Marcel and Lena, were a pair at once. They, when not under the eyes of their watchful mother, had bullied the other children secretly, never letting out it was them. They were bright and happy children around their teacher and friends, but once they were alone, their true personalities showed through.
At the age of eight, the family moved to England, Mikołaj getting transferred to another hospital. The twins were excited, more children to bully in secret. As they had planned, they made friends and charmed the teachers, and got their revenge in secret, no one ever known it was them.
Also at the age of eight, the twins had their first displays of magic, Marcel's was that he turned a broom in a balloon. After three years in England, the twins got their letters to Hogwarts, they were separated for the first time, Marcel being sorted into Gryffindor and Lena into Hufflepuff, but they didn't care, it could be used as a cover.
The twins are currently in their fifth year, and are liking it so far, they haven't been caught for anything they've done yet.
Marcel and Lena are fraternal twins, meaning they don't look alike, and they don't, but they have a faint resemblance to each other. Marcel looks for like his French mother, having her black hair and misty grey eyes. He keeps his hair long, and shaved off one side, thinking that he would look awesome. He likes to dress comfortably, but still fashionable at the same time. He has a fondness for muggle sneakers.
Marcel is a daredevil, he tries things no one else would dare to do, and says things no one else would dare to say. He's prone to swearing, and is not afraid to call you a b*tch in front of a large group of people. He's very arrogant, thinking himself to be more important than anyone. He, however, if you manage to break down his many walls, you will find someone who cares deeply for people very close to him. One characteristic you wouldn't expect him to have is a fondness for children.