The JLS star actually wanted a daughter before the couple had their girls - Alaia-Mai, six, and Valentina Raine, three - but he's excited to no longer be the only male member of the household, and overjoyed for his wife, because she's been longing for a ''mummy's boy'' relationship like he already has with their daughters.
The 'Beat Again' hitmaker also revealed that their eldest, Alaia-Mai, is going to be a great help as she's ''grown up'' enough to be like a ''little mummy'' to her siblings.
Marvin told the new issue of OK! Magazine: ''I'm just so excited!''
He continued: ''I've always been outnumbered in the girl versus boy ratio.
''We've even got a girl dog, Ginger.
''But when we have our son then, yeah, Roch and I will be outnumbered. ''People say you have to ''man-mark'' your kids, so each one has an adult looking out for them.
''Thankfully Alaia's so grown up and so excited to be a big sister, we'll make the most of her help.
She can be like the little mummy.''
Asked if he's excited to have another boy in the family, he said: ''Absolutely. Don't get me wrong, I actually wanted to have a girl first time around so I could have that daddy-daughter thing.
''But Roch has always wanted the mummy's boy thing.
''So for her it's amazing because she's now getting the son she's wanted.''
The pair announced they are expecting a third child together over Easter, and later revealed the gender of their unborn tot by posting a video of their daughters learning the news during an Easter egg hunt.
In the clip, Alia-Mai reads out a note she received from the fictional Easter Bunny, which read: ''Hippity hippity hop, I have great news that I have to drop.
''You and Valentina are such good sisters but now it's time to add someone new to the mixture.
''Now that's all from me, the Easter Bunny, the BIG news is you have a baby brother inside Mummy's Tummy!''
The 35-year-old singer's eldest girl had a big smile on her face as she read the line about the baby and her dad then picked her up, and told her: ''You're going to be a big sister again!''
She then said: ''You're having a baby, a baby boy.''
Rochelle then asked their youngest girl: ''What's in my belly?'', to which she replied: ''A baby brother.''
The 31-year-old beauty captioned the post on Instagram: ''It was an odd Easter but we found some magic in the chaos.
''The Easter Bunny dropped by and sent Marv some back up #AnEasterWeWillNeverForget'' (sic)''
Meanwhile, Marvin admitted it's been challenging wearing many different hats during the coronavirus pandemic, but the family are getting through in their ''own way''.
He told the publication: ''Roch and I have never had a nine-to-five schedule, so we're used to both being at home for a length of time.
''The girls have adapted to homeschooling really well but every day you've got a lot of hats to wear.
''You're a teacher, a dad, a husband, a friend. We're just coping with it in our own way.''
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