handle the changes on combobox in datagridview - C#

Question

I have a datagridview where it is NOT bound to a datasource.

In my gridview I have several columns say four. One of the columns is from the type of DataGridViewComboBoxColumn and the display style is Nothing.

ColumnA columnB ColumnC columnD
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The collection of the column B has three options: 1- Confirmed  2- Declined  3- Pending
in the row that the user is currenlty standing, he can change the selection of the comboBox,
Say, from Confirmed status he changed to Pending so the index has been changed here.

how can I pass the new value and the index of comboBox to store and use it later on the rest of my code?
Which event also I need to fire to apply the changes?