's daughter Isabella is finally kicking back for a much-needed pool day ... after wrapping up her last radiation treatment to tackle her brain cancer.
The 19-year-old posed away with her twin sister Sophia in a series of bikini-clad IG snaps Monday from their sunny vacation ... captioning it, "In good company."
Isabella also enjoyed some R&R at the beach ... smiling wide as she made the most of the break before starting chemotherapy next month.
She said she was excited to be done with radiation during a candid YouTube video last week ... nearly 3 months after doctors found a malignant brain tumor.
She earlier this month her cancer is known as medulloblastoma -- noting docs discovered a tumor as big as a golf ball lodged toward the base of her skull.
Upon the discovery, Isabella underwent emergency surgery at Cedars-Sinai in L.A. ... where she's attending college at USC.
The procedure to remove the mass appears to have been a success.
Her dad dropped everything in NYC at the time ... booking a flight to the West Coast to be by his daughter's side -- which explained why Michael had been off the air so much back in the fall.
Isabella will begin chemotherapy at Duke Children's Hospital & Health Center in Durham, NC, in February.
