My apologies; that was a significant blunder on my part.

Meaning

Apologizing for a serious mistake.

Examples

• John: 'I'm very sorry, Alice. I missed the deadline completely.'<br>
• Alice: '<b>My apologies; that was a significant blunder on my part</b>. Let's discuss how to avoid this in the future.'
• John: '<b>My apologies; that was a significant blunder on my part.</b> I'll explain how this happened.'
• Alice: 'The project budget was significantly exceeded, John.'<br>