Credit: Lester Cohen/WireImage

Just call it Baby Bellamy-Hudson for now!

Dad-to-be Matthew Bellamy was effusive about his "beautiful pregnant girlfriend" Kate Hudson while accepting a Grammy onstage in L.A. on Sunday.

And the Muse rocker, 32, opened up on the red carpet about how he and Hudson, 31, are prepping for their baby's arrival -- and keeping things mysterious!

For starters, the baby's gender "will be another surprise," he told Entertainment Tonight, explaining that they opted out of finding out if it's a boy or girl prior to the big day.

That, of course, makes picking names a little tricky for the couple of 10 months (they reportedly have no plans to marry).

"We're starting to agree on names," Bellamy said. "Hopefully we'll think of something last minute."

The little boy or girl will join big brother Ryder, Hudson's 7-year-old son with ex Chris Robinson. "She is happy for Ryder to finally have a brother or sister," a Hudson insider told Us Weekly last month.