Grohl, 55, did not share any other details about the baby or her mother, and his representatives declined any comment beyond the posting.
Grohl married Blum, a former model turned film and television producer, in 2003. They have three daughters together, including 18-year-old singer Violet Grohl, along with a 15-year-old and 10-year-old.
He was previously married to photographer Jennifer Leigh Youngblood, from 1994 until 1997, and has acknowledged that infidelity helped lead to their divorce.
Grohl started the Foo Fighters in 1994, soon after the death of Kurt Cobain brought an end to Nirvana. In 2022 the band’s longtime drummer and Grohl’s closest friend, Taylor Hawkins, died during a South American tour.