The most common and most likely answer to this crossword clue is the 10 letter word OSTENSIBLE
I've seen this crossword clue in The Times
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More clues leading to the result OSTENSIBLE
- Seeming old and sober — about time
- I set nobles up, it's pretended
- Seeming old, wise to accept retirement at last
- Professed East German deposing sensible leader
- Apparent Opposition leader well-advised to take time
- Professed nothing reasonable over time
- It’s apparent that there is nothing sensible about time
- Seeming ordinary, sober around time
- Seeming old and wise taking time
- Noise belts out that’s apparent
Buddy explains!

The straight part
We know that "pretended" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pretended = ostensible.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 OSTENSIBLE mean?
OSTENSIBLE adjective- Apparent, evident; meant for open display.
- Appearing as such; being such in appearance; professed, supposed (rather than demonstrably true or real).