Would you know anything else about the car that you could tell us, like the model (and MY)?
Sounds like the left brake lamp bulb is blown and the car is using the parking lights as a spare. You would see a fault code at the IC or even a message indicating this.
If it is an older car, then probably your left rear light assembly has lost ground connection and when you brake, the brake lamp "seeks" ground through other bulbs, the parking lamp having higher resistance starts to glow then.
Sounds like the left brake lamp bulb is blown and the car is using the parking lights as a spare. You would see a fault code at the IC or even a message indicating this.
If it is an older car, then probably your left rear light assembly has lost ground connection and when you brake, the brake lamp "seeks" ground through other bulbs, the parking lamp having higher resistance starts to glow then.
