Grandma discovers my secret

Almost a year had passed since that sexually defining night when i watched my grandparents fucking & now i was back staying at their house for a few days. It was all pretty uneventful until the second night when once again i heard grandads deep moaning coming from their bedroom. I tip toed into the bathroom & went to the laundry basket to see what i could find. To my utter delight there was a pair of grans beige sheer pantyhose sitting right on top.
I grabbed them & snuck over to their room. To my anguish though,the door was shut. My heart sank but i was to aroused to turn back. Gently i pushed on the door hoping it wasn't shut properly & to my excitement it wasn't. The door opened slightly & quietly,enough that they didn't notice & enough to give me what i wanted to see & what a wonderful sight it was.
Grandma was on her back in a pair of coffee colored fully fashioned nylons supported by a flimsy balck lace suspender belt & wearing a pair of black strappy high heeled sandals.
Grandad was holding her ankles & thrusting hard into her making her large boobs bounce with each stroke. They were both moaning in pleasure & it was beautiful to watch.
Trembling like a leaf i dropped my pants & scrunched up one toe of her hose then rolled it down over my throbbing cock. It was enough to make me gasp. The reinforced toe was so light yet clung to my swollen glands tightly & judging by how damp it was she mustn't have been out of them long which excited me even further. I raised the gusett of her hosiery to my face & inhaled deeply taking in her flavours & fragrances. I was so close to cumming i didn't dare touch my pantyhose encased cock as i began to suck the juices from her musty gusett.
As my grandparents fucked, i watched in delight as his slick shaft slid in & out of her glistening pussy,her thick lips clinging to his cock. I wanted to be in there on my knees licking his shaft as it appeared from deep inside grandma then kissing her labia as grandad thrust back into her.
As their fucking intensified i began to wank myself imagining grandma's sexy foot inside the hose that was now clad to my cock. The taste of her gusett was one of sheer bliss. I was beginning to precum in her hosiery as grandad continued to pound grandma. She looked incredible in her nylons,sussy belt & heels. Grandad was now ontop of her,with her stockinged legs wrapped around him. His moans were muffled as he buried his face in her heaving globes.
"Cum for me dear,fill me full" i heard her pant as she stroked his head.
I imagined she was saying this to me & as he began to convulse & erupt inside her i too began to cum. I had to suck even harder on her gusett to hide my cries of ecstasy as my cum quickly filled the foot of her pantyhose.
At that very moment grandma looked over towards the door as her own orgasm approached & our eyes meet head on.
For a split second she looked shocked even horrified but then she smirked & licked her lips as the sight of her own grandson masturbating into her pantyhose over her triggered the final release of her own toe curling climax.
As wave after wave tore through her our eyes never once deviated from each other.
My secret was out & it was just the beginning.