Reese Witherspoon was the first person Michael Buble told about his baby.

The 'Haven't Met You Yet' hitmaker and his model wife Luisana Lopilato are expecting a son in August and Michael revealed he was so excited when he found out about the pregnancy, he couldn't resist telling Reese while they were discussing a possible duet.

He told Parade magazine: ''I had just found out [we were expecting]. It was the greatest day of my life, so I just said, 'You know, I'm having a baby!'

''And Reese was so sweet about it and excited for me. It was nice for us to bond that way. I told her before anyone else in the world knew -- even members of my own family!''

Michael, 37 - who married 25-year-old Luisana in March 2011 after over two years together - also revealed his main role during the pregnancy is to tell his wife how wonderful she looks.

He explained: ''Obviously she's doing all the work -- she's carrying the kid. My job, I found out, is just to tell her that those aches and pains are normal [and] that she looks awesome.

''I think sometimes it's probably pretty scary for my wife. It's my job to just be strong for her like she's strong for me all the other times.''