Chances are that you've seen one before. Dunnocks are regular garden visitors all across Europe and Asia. That you didn't notice the bird, is because it prefers to live hidden in the undergrowth. That, and its plumage is a sober greyish brown. You probably thought it was just another sparrow.
But if there's one thing we have learned from day-time talk shows, it's that the most unnoticeable ones lead the most interesting lifes. Although dunnocks usually form pairs, not every bird is a fan of monogamy. And it's often the woman who does the cheating. Sometimes such a mischievous female mates with two males. The male knows that female dunnocks can't be trusted, so he pecks her cloaca clean before mating. Unfortunately for him, that doesn't always work. Chicks in the same nest regularly have different fathers. Since neither can be certain that the nestlings aren't his, both will help rearing the young. Quite an example for many homo sapiens, huh?
Next time you think you see a sparrowlike bird in your garden, check if it's a dunnock. Maybe you get a glimpse of the soap opera life this anonymous bird is living in your hedge.