Images show the shocking condition a flat was left in when tenants moved out including mountains of rubbish and piles of faeces.
Landlord Lee Locking had been renting out the property for the past five years and, when he received the keys and returned to the flat, found every room was piled high with rubbish.
The shocking scene of debris included mountains of rotting food, cat faeces in the bath and piles of bags filled with cans and bottles.
The WalesOnline photographer that went to the property described it as the "worst place" he had been in his 20-year career.
The landlord said he felt let down by the letting agent who managed the property, adding that he felt they should not have allowed the flat to get to that condition.
Lee claimed the tenant told him that he could keep the deposit for the flat to cover the mess, but the landlord was shocked to see the extent of it.
Now, Lee, 56, faces the daunting task of making the property in Swansea liveable, which will include a new bathroom, new kitchen and new carpets, not to mention disposing of what he said are the three to four tonnes of rubbish left behind.
Lee said every time he steps foot in the house in Waunarlwyfdd, it leaves him feeling dirty.
He said: "Every single room is a state. I can't even go in without wanting to shower immediately after.
"When I first went to the property, I'd taken the dog with me. I opened the door and the smell just hit me.
"I took one look at the mess up the stairs and closed the door and put the dog back in the car, because there was no way I was letting the dog come in.
"I have no idea where the person slept. A neighbour said they saw the tenant take a mattress from the house and assumed it was being taken to the tip.
After seeing the state of the property, I'm not so sure."
Each and every room in the property is filled to the brim with some sort of mess.
The kitchen contains jars and boxes of rotting food, a litter tray which is piled high with faeces, and empty cartons of milk.
In one of the other rooms, the floor is not visible, covered in bin bags, takeaway containers, Amazon boxes and clothes.
The bathroom is one of the worst rooms in the house, with the bathtub covered in old cat faeces.
The toilet seat is just about hanging on to the bowl, while the toilet is filthy, and surrounded by old plastic bags, used tissue and empty food packets.
When the tenant handed over the keys, Lee claims he was told that he could keep the £400 deposit to "take care of the mess".
But Lee reckons the cost of making the place liveable again will be much higher.
He said: "It'll easily cost me a few thousand, I'll need to replace all the carpets, the kitchen, the bathroom. I've been told there is at least three to four tonnes of rubbish to clear. I'm at breaking point with it."
As Lee has no previous experience with renting, he decided to entrust the property to be managed by letting agents, John Francis.
Lee says he feels let down by the company, and claims that they should not have allowed the flat to get as bad as it has.
"I understand that people may struggle with their mental health, and keeping on top of cleaning might be tough for them, and I really feel for them, but John Francis allowed it to get to this state."
Lee continued: "I feel really annoyed and angry that I've let them manage my property for the past five years and this is the state it's been returned to me in.
"They were supposed to vet the tenants and be the main point of contact for any problems. The flat was meant to be no pets allowed but there has clearly been a cat in the property.
"They've taken 12 per cent plus VAT for five years and now they've left me in limbo."
A John Francis spokesperson said: "John Francis Lettings takes any customer complaint extremely seriously. We are in receipt of an official complaint from the landlord and which we are currently investigating.
"We will liaise directly with the landlord to resolve the issues."
