Yup i purchased a Seville Orange about a year or so by mistake as i had wanted a regular orange and didn't realise it was a bitter orange suited pretty much only for marmalade purposes. I thought i'd wait and taste it first before swapping him out of my citrus patch as the fruit might be ok but finally had a ripe fruit to try today and it was not pleasant!
So i brought a new Mandarin "Burgess Scarlet" to replace it and will give the serville to my mom who likes making marmalade.
Has anyone grown this variety? Sounds like its an old fashioned type flavour similar to a clementine.
Sad to let a friend go

Why not just keep the seville as an ornamental tree, if it's your friend?

I might be wrong but I think they use this as a vigorous rootstock. If so grow some and try your hand at grafting

Seville is the primary rootstock we use on about all our citrus, this last year I started using C-22 in a limited amount..

Graft your tree over to what you want ..

Not a bad idea to graft something else onto it. I have already pulled him out of the raised bed he was in and in his place put the mandarin. I have stuck him into a container so if my mom doesn't want him i'll give the grafting a try. I tried a cleft graft two times but with no success so it would be good to give it another go. Maybe this time a T bud graft which seems to be the prefered way??

The trick to cleft is to align the cambiums on one side or the other or both if they Match in size also wrap the graft once then rubber band it to keep it tight and a wrap over that. The scion only wrap once.
But t bud is by far the easiest just make sure the bark is slipping.
Sorry for rambling but lmk if you need any other explaining.

Thanks for the tips David. My first attempt was in retrospect quite amatuer. For starters my knife wasn't sharp enough (it was a serrated kitchen knife!) i did use parafilm but not the entire length of the scion just then join area. I did ensure the cadmium layers were matching but i think because the cut was rough it failed. Will have to give this another go i think.