Military career

Henry Knight Gregson Jr. was the third son of Henry and Eliza Mary KG. Lilian Caley found the attached military record for Henry Jr. on the National Archives website (UK).  Henry began his naval career at age 13 as a cadet on HMS  Britannia in Portsmouth Harbour. He served on many vessels and retired as Lieutenant, Royal Navy.

Link to: Service Record of Henry Knight Gregson, Jr.

Searching the web, I came across a reference to Henry Knight Gregson, Royal Navy Lieutenant on the web site of the "Royal Collection Trust"(royalcollection.org.uk).  It would seem that the photograph of Henry shown in his naval uniform is lodged in the Royal Collection for the reason explained below, and I quote from that web site:

"Acquirer: King Edward VII, King of the United Kingdom (1841-1910), when Albert Edward, Prince of Wales (married) (1863-1901)

Provenance:
Presented to King Edward VII when Prince of Wales by the Captain and Officers of HMS Serapis, in remembrance of his voyage to India and back in the ship (1875-1876)

Description:
Photograph of Henry Gregson, three-quarters length portrait; sitting, in Royal Navy uniform, helmet on stand to left."

The photograph's reference number is RCIN2583983.  Unfortunately, when you search the Collection, one is told the photograph is not available.

However, the description clearly corresponds to the photograph displayed on the Forum and concurs with Henry's Military record where it is shown that Henry served on the Serapis from 22 July 1875 to 24 May 1876.