The 47-year-old actor's daughter Cassandra Estevez recently welcomed a baby girl named Luna.
The 28-year-old is the child of his high school girlfriend, Paula Profit, who has also gone by the name Paula Speert.
Cassandra's pregnancy was reported in January.
Charlie now feels that his rundown of moments to achieve in his life is almost complete thanks to the new addition to the family.
"It's impossibly a most wondrous day," he told TMZ. "My bucket list is a thimble!"
The announcement means Charlie's twin boys with former spouse Brooke Mueller have become uncles aged four.
Bob and Max are currently in the temporary care of Charlie's other ex-wife Denise Richards.
The decision came after the Los Angeles County of Department of Children and Family Services deemed Brooke a danger to herself and others and was involuntarily confined.
She subsequently entered rehab for the 19th time due to her drug addictions.
Now Denise apparently wants the kids to remain with her and their half-sisters Sam, nine, and Lola, seven.
"The twins are a part of Denise's family, and they love being with their sisters," a source told Radar Online.
"It's a very happy household. It gets a bit chaotic, but Denise can handle it."
Apparently Denise is prepared to formally seek permanent guardianship over the young brothers.
Charlie feels his boys are safe in Denise's care.
"Charlie is 100 per cent supportive of Denise raising the twins, and he feels she would be the best possible mother they could have," the insider revealed.