string concatenation issue

$UserLastNameGlobal="James"
$UserFirstNameGlobal="Bond"

Write-Output "Folder $UserLastNameGlobal" + "_" + "$UserFirstNameGlobal already exists"

=Bond already exists

Write-Output "Folder $UserLastNameGlobal_$UserFirstNameGlobal already exists"

=Folder Bond already exists

I need output Folder "James Bond already exists". I tried above 2 different ways and it is not getting what i want. Please help