It looks like a day lily, some have come up in my garden but they're orange, but I don't remember planting them. Each flower lasts for just one day, apparently.
It's definitely a day lily and live up to that name as they only flower for one day but if you remove the old ones you will get constant flowers for a long time. Had these in my last garden and would have a daily wander with a cuppa and snip them off by hand. If you leave the old flowers on, eventually the old flowers are replaced by roundish seed heads which don't look nice and result in less flowers. Rather do the daily deadheading which takes minutes and have repeat flowering