非常巧，我在张道真的《初级英语词典》上查到了你的这个句子：

It’s the darlingest puppy I ever saw. 这是我见过的最可爱的小狗。

但是对于这个用法，我也持怀疑态度，因为以ing结尾的分词形容词原则上是不能通过加词尾er, est 来构成比较级和最高级的。比如剑桥大学出版社出版的《英语教师语法》（Ron Cowan原著）就有这样的说明：

Participial adjectives have comparative and superlative forms only with more and most and with less and least. They cannot add -er and -est, as is illustrated by (6b) and (6d).

(6) a. That was the most amazing performance I've ever witnessed.

b. *That was the amazingest performance I've ever witnessed.

c. When she heard that the plane was overdue she became even more worried.

d. *When she heard that the plane was overdue she became even worrieder.

e. I couldn't be less concerned.

f. Of the many solutions to this problem, his is the least promising.