A MUM has been left fuming after her ex dropped off the wrong baby.

The anonymous woman, believed to be from the U.K., took to Reddit to explain how she was in the middle of a work call when her son’s father dropped the 17-month-old baby at her house, U.K.-based Mirror reported Tuesday.

And it was only when the baby started crying 10 minutes later that the mum made the shocking discovery — this wasn’t her baby.

She said: “I immediately noticed that this was not my son, as my son has blue eyes, and this baby had green eyes.”

She explained that her ex Sean also has another son with a woman who she called Lydia, who is only six weeks younger than her child, so he’d accidentally confused the two as they lay sleeping in their car chairs after a day trip out.

For the first year of the babies’ lives, their respective mums had full custody and their dad visited on a regular basis.

But after they turned 1, Sean got 50/50 custody.

The mum added: “This means Sean has both boys at the same time.”

This arrangement had only been in place for around for five months when he made the mistake.

When she called Sean telling him to return her baby to her, he was only 10 minutes away on route to Lydia’s.

“It was the worst 10 minutes of my life but Sean came back smiling, carrying my son, and says in the most condescending tone of voice ‘see? He’s fine. No harm done.’

“I told him that we are fixing this custody agreement. He is not having both boys alone again.” But Sean thinks she’s being “unreasonable.” He tried to argue that it’s an easy mistake to make.

“Sean won’t get any time to himself if he has Lydia’s son on even weeks and mine on odds, meaning that he’ll be more exhausted and it will decrease his income as he won’t be able to work overtime (which he currently does in his weeks without the boys).

She asked people on Reddit for their opinion. The majority of users voted that she was unreasonable because “parents make mistakes.”

One said: “If both kids were asleep in the car and he didn’t want to wake them up and leave the child resting that would explain why he didn’t see the eye color. It sounds like an honest mistake that I bet he never makes again.”

Another wrote: “As a mother myself I can completely understand how scary and stressful those 10 minutes were.”

(SD-Agencies)