Singer/songwriter Bruno Mars started off 2011 in style by celebrating his second number 1 U.S single. 

His track 'Grenade' soared to the top of the Billboard chart after fluctuating at different positions for the past thirteen weeks, which put him ahead of Katy Perry's 'Firework' and Ke$ha's 'We R Who We R'.

Mars tweeted:

Grenade is the #1 Song in the country Thanks to you guys! What a way to end my year. Thank u all for giving me the greatest year of my life!

Watch him perform 'Grenade' as part of a live session here: