Transfer of jointly owned property from father 2 son jointly owned

I bought a flat before marriage and therefore added my fathers name as a joint owner. My father is 90 and therefore wants to ensure that after his demise that I get sole ownership. I have 2 siblings but they are honest and have no intention in it. Do we need to make a gift deed or will the flat automatically be in my sole ownership after fathers death? My father has clearly specified in his will that I will have sole ownership after his death and no persons has any rights to the flat. Thank you.