Mould behind radiator

I've just bought a new house and went to start the prep for painting one of the bedrooms. I took the radiator off to discover it was mouldy behind. I didn't realise it was lined with paper. Is there an easy way to fix this without having to re-paper the whole room? Suggestions would be greatly appreciated.
Thanks

Mountain mj, good evening.

I assume this house is new to you, not actually a new build?

Was it empty for a considerable time prior to your purchase?? at a guess about one year perhaps??? [pure guess]

If it was empty for a long time, condensation would be a first consideration, especially if the heating was switched off for a long time??

As for a "fix" for the damaged lining paper? simply cut away the stain damaged paper BUT, within the area that the Rad occupies so any patch cut lines are very difficult to spot.

Is that area of wall still damp? Sellotape a square of clear plastic film on to the paper an area of film of about 150.mm / 200.mm Square and see if any water forms of the inner surface of the film.

Ken.

Yep. It's a Victorian house. It's not been empty at all really.

I'll give your solution a go. Thanks Ken

Mountain mj, good evening, again.

Another go at this ?

If??? the bedroom was not in use??? the Rad may have been switched off and Condensation could have formed behind the rad? especially if there was a bed hard up against the rad??

Ken.