Combobox to select existing customer and populate userform text box's

Hi,

I have a userform. On this form I have many text box's for customer details.

customer box.jpg

The button "New Customer" works. It uses the following code to add a new customer id number.

Private Sub CommandButton8_Click()
Me.TextBox21.Value = Format(Application.Max(Sheets("Customers").Range("A:A")) + 1)
End Sub

What I would like is, for the combo box (ComboBox1) to show the First name and last name of existing customers, from the "Customers" sheet.

customer sheet.jpg

Then, when I select one, their details are used to populate the userform.

Customer details.jpg