What song did Sarah Brightman sing (as a duet) at Diana's concert.?

Question:

What song did Sarah Brightman sing (as a duet) at Diana's concert.?

It was on in the background where I was but too much else was going on to recognise it

thanks

Best Answer - Chosen by Asker: Sarah Brightman sang "All I Ask of You" with Josh Groban. "All I Ask of You" is the duet from Phantom of the Opera between Christine and Raoul...not with the Phantom.