还真没看出来。(Hái zhēn méi kànchūlai.)( I ) really did not see it!

Explanation

“还真没看出来”表示因发现或被告知了以前没有注意到的事情而感到吃惊，根据不同的语境，可以表示褒义也可以表示贬义。
“还真没看出来” means the speaker is very surprised when he/she finds or is told something hasn’t been noticed . It can indicate commendatory or derogatory according the different situations.
Words:

第一名dìyì mínɡ:the first prize;
聪明cōnɡmínɡ:clever.

Sentences

1、Jiă: Lǎo Lǐ de érzi déle Shùxué Àosài dìyīmíng!
甲：老李的儿子得了数学奥赛第一名！
A: Lao Li’ son has won the first prize in Mathematic Olympic Competition.

Yǐ: Zhēnde a, hái zhēn méi kànchūlai tā érzi zhème cōngming ne!
乙：真的啊，还真没看出来他儿子这么聪明呢！
B: Really? I did not see how clever he was!

2、Jiă:Wǒ zuówan yíxiàzi jiù bǎ jìhuàshū xiěwán le.
甲：我昨晚一下子就把计划书写完了。
A: I have finished the plan in a moment yesterday evening.

Yǐ: Hái zhēn méi kànchūlai nǐ zhème lìhài ya!
乙：还真没看出来你这么厉害呀！
B: Really did not see it!