It looks to me like a banana.

Looks like either Musa velutina or one of the Purple Ornata bananas. Definitely not a heliconia

Thank you. I wonder where it came from. I have planted lots of Mussa coccinea but haven´t seen this before.

The tiny little "bananas" circling the flower are probably the culprits...they are full of seeds when they ripen. You muct have gotten a hitch hiker somehow, either carried in with another plant, dropped by a bird or other animal, or some other mode of transport. Its lovely though!