Tile blocked bathroom window

[Cellomusic]

In middle of bathroom renovation. Have the plumber but doing the tiling myself. The window is now blocked up with brick on the other side and shower will fit fitted so old window will be in the shower so need to make it waterproof. How can I best tile the old window area? Seen something called tile backer but do I need to fit anything else underneath it? Remove the old window itself or leave in place....?
Thanks...

What other side? Do you mean the outside? How can you block a window up without removing the frame?
I've done plenty of DIY in my time but just can't envisage what you're talking about.
Not sure if photos are allowed again now after this weekends incident but if you can I think you need to post some.

Thanks for reply. Yes blocked up on the outside wall by building another room onto the house there and a wall across the (previous) outside of the window! 🙂 Don't seem able to add photos ATM but the window frame is still in place... I think possible to remove it from the internal room. But maybe better to leave in place and board over with something...?