The most common and most likely answer to this crossword clue is the 15 letter word YELLOWSUBMARINE
I've seen this crossword clue in The Guardian
Y
E
L
L
O
W
S
U
B
M
A
R
I
N
E
Buddy explains!
The straight part
We know that "one animated" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one animated = yellowsubmarine.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.