Conversation so far:
What are some of Josh Groban's famous performances?
On January 18, 2009, Groban performed as part of the Presidential Inauguration ceremonies
What songs did Josh Groban sing at the 2009 Presidential Inauguration?
performing My Country 'Tis of Thee in duet with Heather Headley

Question: Has he ever performed with other famous singers?
Self-contained rewrite: Has Josh Groban ever performed with other famous singers?