A pregnant Instagram influencer and her former stepson have tied the knot and suggested their unborn baby "looks like" a boy in a new ultrasound video.

Marina Balmasheva, 35, and Vladimir "Voya" Shavyrin, 20, got married during an "ordinary" ceremony in a registry office just months after she went public with their relationship, sparking a backlash.

Her ex Alexey Shavyrin claims Marina and his son began an affair while he was still married to her and he discovered it when he heard them having sex in a bedroom in the family home in Russia.

The love triangle set off scandalous headlines in their homeland, and Marina has previously told how she cried and shook with joy when a pregnancy test came back positive.

Marina Balmasheva, 35, and Vladimir "Voya" Shavyrin at their "ordinary" wedding ceremony

In a new video for her 433,000 followers on Instagram, Marina and Voya, from Slavyansk-on-Kuban, sign their names in a registry office and are declared husband and wife as soft music plays in the background.

As they turn and face each other, they peck each other as they kiss and hug, with Marina smiling and rubbing her second husband's back as she faces the camera.

In the caption, Marina described the video as "ordinary" and said there was nothing lavish about the event.

Marina and Voya began an affair when he returned home from university
An ultrasound image that Marina shared on Instagram last month

She said they drove to the office themselves and left their rings in the car as they got married.

She wrote: "There was a good mood and embarrassment.

"We are some kind of lunatics in the video.

"I declare us husband and wife."

Marina posted this photo after surprising Voya with the pregnancy test result
Marina cried and shook after finding out that she was pregnant

She also told how they celebrated their union later in the evening.

The wedding video was posted after she shared new ultrasound footage that shows the foetus moving.

Marina revealed the baby "looks like" a boy, measures 5cm (just under 2ins) and she is 11-12 weeks pregnant.

She said she was overcome with emotion as she watched her unborn baby move in the womb, but Voya did not cry.

Marina has been giving regular updates about the couple's relationship and her pregnancy since she announced they were together as a couple.

Marina became an Instagram influencer as she showed off her 8st weight loss
The mum has faced a backlash over her relationship with her former stepson

Marina's ex-husband, who is now raising their five adopted children alone, claims she seduced Voya and he would have forgiven her for cheating on him if it wasn't his son.

Alexey claims she would leave their bedroom in the night and have sex with her stepson in an adjacent room.

He claims he once heard them having sex and she then returned to her marital bed and lay down next to her husband.

Marina has shared photos of what she used to look like before losing weight
Voya's dad claims he could hear his wife and son having sex at night

Alexey said he demanded a divorce, which was granted, and Marina ditched him for his son.

Marina and Voya's sexual relationship is said to have started after he returned home from university when he was 19.

She had been his stepmother since he was seven.

Marina became an Instagram influencer as she showed off her 8st weight loss.

She has gained thousands more followers after revealing her relationship with Voya and announcing her pregnancy.