The most common and most likely answer to this crossword clue is the 5 letter word BLUES
I've seen this crossword clue in The Daily Telegraph
B
L
U
E
S
Buddy explains!
The straight part
We know that "Royal Horse Guards/music" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case royal horse guards/music = blues.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BLUES mean?
BLUES noun- The colour of the clear sky or the deep sea, between green and violet in the visible spectrum, and one of the primary additive colours for transmitted light; the colour obtained by subtracting red and green from white light using magenta and cyan filters; or any colour resembling this.
- A blue dye or pigment.
- Any of several processes to protect metal against rust.
- Blue clothing
- (in the plural) A blue uniform. See blues.
- A member of law enforcement
- The sky, literally or figuratively.
- The ocean; deep waters.
- The far distance; a remote or distant place.
- Anything blue, especially to distinguish it from similar objects differing only in color.
- A dog or cat with a slaty gray coat.
- One of the colour balls used in snooker, with a value of five points.
- Any of the butterflies of the subfamily Polyommatinae in the family Lycaenidae, most of which have blue on their wings.
- A bluefish.
- An argument.
- A liquid with an intense blue colour, added to a laundry wash to prevent yellowing of white clothes.
- A type of firecracker.
- A bluestocking.
- One of the three color charges for quarks.
- (usually in the plural) A feeling of sadness or depression.
- A musical form, African-American in origin, generally featuring an eight-bar or twelve-bar blues structure and using the blues scale.
- A uniform made principally of a blue fabric.
- Any of a number of sports teams which wear blue kit.
- To make or become blue.
- To treat the surface of steel so that it is passivated chemically and becomes more resistant to rust.
- (laundry) To brighten by treating with blue (laundry aid)
- To spend (money) extravagantly; to blow.