* Duke of Edinburgh has been in hospital since Tuesday
* Precautionary stay expected to last into next week
* Philip felt ill but ailment is not related to COVID-19(Updates with end of visit, Princess Eugenie)
By Toby Melville
LONDON, Feb 20 (Reuters) - Prince Charles, heir to theBritish throne, on Saturday visited the hospital where hisfather Prince Philip is being kept as a precaution after feelingill, a Reuters photographer at the hospital said.
Charles arrived at the back of the London hospital wherePhilip, the 99-year-old husband of Queen Elizabeth, has spentfour nights. Charles was at the hospital for just over half anhour before departing.
Philip, the Duke of Edinburgh, was admitted to hospital onTuesday as a precautionary measure after feeling ill with anailment that is not related to COVID-19.
He is expected to remain in hospital until next week, aroyal source said on Friday, adding that doctors were acting outof an abundance of caution and the duke remained in goodspirits.
Both Philip and the 94-year-old queen received their firstdose of the COVID-19 vaccine in January.
He spent four nights at the same hospital at the end of 2019while being treated for a pre-existing condition.
Philip is now rarely seen in public. He stepped down fromofficial engagements in August 2017 after completing more than22,000 solo events and thousands more alongside the queen.
A former naval officer renowned for his sometimes brusquemanner and humour, Philip married Elizabeth in 1947, five yearsbefore she became queen. He is now by far the longest-servingconsort of any British monarch.
In an apparent tribute to the duke, one of hisgranddaughters, Princess Eugenie, and her husband JackBrooksbank said on Saturday they had named their first sonAugust Philip Hawke Brooksbank.
(Reporting by Toby Melville, writing by Alistair Smout, editingby Mark Heinrich and Giles Elgood)