I Didn't Think They'd Do It, And I Didn't Think I'd Enjoy It?

My wife just asked me if I wanted to join her in the shower.

Great you might think but the only problem is my dad is here. I rather boringly have been watching the last of the Olympics so I refrained my dad was snoozing in the armchair after Sunday dinner.

Bev went upstairs, my dad opened his eyes and said are you going to get in the shower with Bev.?
I told him to keep out of things, he said Son ill give you one minute to get up there or I'm going to go up and try my luck. The silly sod looked at his phone and said I'm not joking, if Bev is prepared to offer you a joint shower with me here then she's horns and if you ain't going to do anything about it then I will try my luck.

I will be honest this talk was turning me on, I said " go on then, knock your self out, don't be surprised if she knocks you out!"

Then he trots up the stairs and tries the bathroom door and it's not even locked. He walks in and I see the lock spin round from outside as I follow behind him.
The bathroom door is lock and my father is inside with my naked bath.
I immediately clamp my ear to the door and Bev what's going on. Dad says I need to pee.
Bev says 'fucking hell John! "

And my dad says yes that's for you I'm going to fuck you so hard or tell me to go . Then I literally hear them fucking and even before either of them has I've cum and cum in my hand. I'm so embarrassed I decide to go and get petrol for the morning.

When I get home Dad's gone and Bev is gardening. Nothing is said.

What do I say?