How to prepare party for a planned Character Death

I’m a newish DM, have been doing it on and off for about 2 years now. One of my players wants to have a scripted character death at the beginning of the next session. They already have a new character made. The issue comes with actually executing the death. I am playing with new players. This is the first campaign for 4 of the 6 players. One of the experienced players is the one whose character is going to die.
My biggest concern here stems from my own experience as a player. There was a planned character death with no warning and I completely blamed myself and got very upset. My character tried to do so much to help but nothing was successful. The DM could tell I was getting upset but kept going until that scripted character died. I cried, I was so upset. After the session was over I talked to the DM and the player and profusely apologized to the player for letting the character die. Only to be told that the whole thing was planned so that the new character can be brought in.
I don’t want to ruin the experience and break the immersion for my players by telling them in advance but don’t want to upset anyone either.
Any suggestions from people who have done this before is appreciated.