4 year old separation anxiety

[Wilish]

Help please,

My 4 year old (nearly 5) has recently stopped wanting to go to his dads, his main reason is because he will miss me, so it's a separation anxiety thing. He doesn't mind going to school or party's etc just screems and shouts when I tell him he is going to his dads. I've tried to prepare him by telling him on advance to prepare him but that doesn't work. I'd appreciate some advice.
FYI he is a twin and his brother is happy to go.
I've asked him if anything has happened to stop him wanting to go but he says no.

Hi,
this is just my opinion, I’ve worked with a lot of older children regarding this but maybe you could apply the same to your son. If you have an okay relationship with his Dad where you can talk honestly perhaps share with him that your son is saying this, it could just be stage he’s going through. I don’t think forcing him to go would be the right thing to do but his Dad needs to know it is his son’s choice not yours if that makes sense. Could he go to his Dads just for the day and come back for the night? Or could you take the twins out together? Again I don’t know what your relationship with Dad is like.