Check if sheet exist based on drop down list

[oerberg]

In cell D12 I have a drop down list, I have written a macro that allows me to create a new worksheet and taking the name from the selected name in the drop down list.

My issue is that I want to make an error check to see if worksheet has already been created, however I am stuck in the first part, can anyone help me get unstuck?

 Dim ark As String
    ark = Sheets("Forside").Range("D12")
    
    If Not SheetExist(ark) Then
    
    Sheets("Standard").Select
    Sheets("Standard").Copy Before:=Sheets(3)
    Sheets("Standard (2)").Name = Sheets("Forside").Range("D12")
    
    Else
    MsgBox ("ark already exist")