Barclays'
Barclays said he will leave with immediate effect.
Del Missier has for years been a key lieutenant of Diamond, helping him build up the Barclays Capital investment bank, and was appointed COO last month.
Diamond resigned earlier on Tuesday in a sudden move after a record fine for the bank over its manipulation of Libor submissions.
"I have every confidence that the Board and Executive Management of Barclays will be successful in executing their plans, and I wish them the best of luck in doing so," del Missier said in a statement.
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