Friday afternoon and no-one was at the office except for me and our receptionist who was working late to catch up with some filing. I went to go and collect a printout at reception and when I walked in there was Nathi bent over the copy machine. We were on very good terms and I had often talked with her about private matters, although certainly never anything intimate. I had never flirted with her before either, however, her large buttocks outlined by her skirt that was pulled tight from the position she was in looked very alluring from my angle and I felt my cock stir. Knowing I might well regret it later, I still couldn't resist a little quip, "Paper jam? It should happen more often." She immediately guessed that I was admiring the view and responded, "So you like what you see?" "Yes, it looks good from where I'm standing," I replied. "Thank you," she said, "it's always nice being complimented by an attractive man." I blushed a little and felt my cock strain more against the fabric of my trousers. She of course didn't notice as she was still bent over the machine. She had, however, stopped fiddling with it. What the hell I thought, forgetting the possible unwelcome consequences that might ensue should this go wrong and I allowed my hand to gently brush over her buttocks. She pushed back towards my hand and wiggled a little to the sides. I allowed my fingers to linger and gave a little squeeze and when she murmured softly and again pushed back into my hand I took it is a signal to continue what I was doing. I ran my hands down her thigh and then up end her skirt, feeling bare skin all the way up to her buttocks. I started massaging and while doing so she pulled up her skirt giving me a full view of her large, well rounded, chocolate brown derriere and a white g-string. So she was wearing underwear, albeit very skimpy underwear. I moved my right hand between her legs, and pulled her g-string aside, feeling the smooth shaven bulge of her large mons veneris. She shifted her weight slightly, leaning forward and pushing her butt upwards to give m better access and I slipped first one and then a second finger inside her dripping wet pussy. She moaned and started sliding backwards and forwards on my fingers. With my other hand undid my trousers and allowed them to fall to the ground. I pulled my underpants down and my cock sprang out at attention, throbbing and huge, the biggest, hardest erection I had had in ages, veins bulging and my cock head almost glowing. I removed my fingers from her pussy and allowed my cock to slide into her. She murmured with pleasure and said something like, "Mmm, so it's not true about white men being small." I pumped hard with my hips, while she pushed back against me, her incredible wetness making a rather sloppy sound. She screamed out and as I was about to cum myself I pulled out and squirted onto her buttocks, my glistening white pearls contrasting with her smooth brown skin.