A blonde bombshell.

You peek in. A big breasted blonde girl is kneeling next to your mother's lap. Cock in her mouth. Her head is being guided by your mother's hand. She moans much louder than she did before. Your surprised the blonde could take in that much meat. Your mom has always had a large cock. You've heard snippets of conversations of her and toe other mom bragging about it. Now you can see what they was talking about. It looks to be about eleven inches long and about as thick as your wrist. But damn! That girl is taking all of it down her throat!
Your hands pull your own dick out and start stroking. Precum makes your job easier. You start fast and plan to continue at that pace if not go faster. A soft noise is made with every stroke. You get lost in the feel of your own hand and, stupidly, lean against the open door. You fall into the room. Both people in the couple jump, the blonde still sucking your mothers monster.
"Honey, what are you doing!" she says. Then she sees your slick cock and blushes.
"Uh, nice cock?" you say, hoping compliments will work to get you out of this mess.
"Thanks? You've... Grown." she says, "Gwen," She motions to the girl sucking her off, "This is my daughter." Gwen pops her head off of the giant, and smiles.
"The one with the cock?" she says, then looks to your mom, "Can she join?"