He said the Duke may choose to limit his participation at the events he does attend.
In December, the queen was forced to cancel public appearances and missed Christmas mass due to a lingering cold, and the prince also fell ill the same month, the New York Timesreported.
May paid tribute on Thursday to Philip for his contribution to Britain and beyond, his "steadfast support" of the Queen, and his patronage of hundreds of charities and good causes.
"I didn't get to speak to Prince Philip very much but it was a very special day".
Prince Philip has accompanied the Queen on all major foreign tours, including three visits to India.
Outspoken, irascible and intensely private, Philip, a Greek-born former naval officer, developed a reputation for brusque comments and occasional gaffes at some of the thousands of ceremonial events he has attended.
The Queen's public schedule will continue as normal but it is understood other members of the Royal Family will "step up" in support of the monarch.
The announcement was made after all members of the Queen's household were gathered at Buckingham Palace for a highly unusual staff meeting.
The Prince Phillips is patron, member or president of more than 780 different organizations, Whereas, he will not be attending the meetings and engagements actively.
Many speculated on what the royal family expected to announce on Thursday morning, May 4th.
Berthelsen said the public is expected to see a lot more of the Queen's son, Prince Charles, as well as the younger royals next fall.
He once admitted the curtailment of his career was "disappointing", but said that "being married to the queen, it seemed to me that my first duty was to serve her in the best way I could".
Close confidants of the royal family said the decision was a personal one taken by the Duke himself, who may now devote his time to writing his memoirs.
Elizabeth and Philip celebrate their 70th wedding anniversary in November.
- The Right Place for Drug Rehab
- Oil Inventories Fall More than Expected; Prices Rise
- Jeurys Familia Has Clot In Throwing Shoulder
- Kings' Rudy Gay to opt out of final year of contract
- Predators get extra rest in this year's playoffs
- Pentagon: Islamic State's Afghan leader killed in April raid
- Talent Not an Issue for England's New Manager
- Trump says meeting with Russia's Lavrov was "very, very good"
- Top smartphones for gaming
- Aetna leaving Affordable Care Act market in Nebraska