The most common and most likely answer to this crossword clue is the 3 letter word KIN
I've seen this crossword clue in The Sunday Telegraph
K
I
N
Buddy explains!
The straight part
We know that "relations" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case relations = kin.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 KIN mean?
KIN noun- Race; family; breed; kind.
- Persons of the same race or family; kindred.
- One or more relatives, such as siblings or cousins, taken collectively.
- Relationship; same-bloodedness or affinity; near connection or alliance, as of those having common descent.
- Kind; sort; manner; way.
- Related by blood or marriage, akin. Generally used in "kin to".
- A primitive Chinese musical instrument of the cittern kind, with from five to twenty-five silken strings.
- A day, in the Mesoamerican Long Count calendar.
- (auxiliary verb, defective) To know how to; to be able to.
- (modal auxiliary verb, defective) May; to be permitted or enabled to.
- (modal auxiliary verb, defective) To have the potential to; be possible.
- (auxiliary verb, defective) Used with verbs of perception.
- To know.
- To seal in a can.
- To preserve by heating and sealing in a jar or can.
- To discard, scrap or terminate (an idea, project, etc.).
- To shut up.
- To fire or dismiss an employee.
- To hole the ball.