Lily Collins is officially a new mother ... welcoming her first child to the world via surrogate earlier this week!

The longtime film and TV star's surrogate gave birth earlier this week in Northern California ... and just posted about the baby a moment ago ... sharing a picture showing the little baby in a blanket with her name -- Tove -- written in gold letter on a white blanket.

She wrote in the caption, "Welcome to the center of our world Tove Jane McDowell. Words will never express our endless gratitude for our incredible surrogate and everyone who helped us along the way. We love you to the moon and back again…"

Lily is married to Charlie McDowell -- son of a pair of Golden Globe winning actors, Malcolm McDowell and Mary Steenburgen, and stepson of sitcom legend Ted Danson. Lily is the daughter of legendary English drummer Phil Collins.

We're told Mary and Ted were spotted visiting the baby in the hospital shortly after the kiddo was born.

Sources in the know tell TMZ ... the couple is overflowing with love and gratitude at the arrival of their very first kid.

Collins and McDowell married back in 2021 after first becoming romantically involved in 2019.

While we didn't know about Lily's pregnancy, we do know they've planned to expand their family for a while now ... 'cause back in October, Charlie told E! News they wanted to take the leap into parenthood -- though clearly he hid the fact that the baby was on the way.

Congrats, Lily and Charlie ... parenthood might not be a vacation, but it's definitely an adventure!