Staying With Sister

For context I'm F45 - About 30 years ago now I was around 14 or 15 and staying for a few days with my sister and her husband. I always thought that he was handsome and used to fantasize about kissing him, him touching me and of course seeing him naked. One night I was lying in bed, not sleepy, and I heard the unmistakable sounds of sex coming from their room. My bedroom door was slightly open so I got up to peek through the gap but of course their bedroom door was shut, I was transfixed imagining what was going on and thinking about his hard cock. After a few minutes I heard him grunt as he finished. For some reason I stayed looking at their door when it opened and he walked out, naked, to use the bathroom. My eyes nearly popped out as I saw that his cock was still half hard and to me, looked huge. He didn't notice as I swiftly moved back and closed my door. My finger and pussy got a good workout that night and many times after.