《韦氏词典》和《柯林斯高阶词典》均提及despair可用作及物动词，不过这种用法已被废弃。例如：

(transitive) obsolete

to give up hope of; lose hope in

从英英释义末尾的介词可知，及物动词despair后接名词，意为“对...感到绝望/不再抱希望。

但现实语言中，确实有despair后接that从句的。例如COCA语料库有如下例句：

Rodiles despairs that there will be no such American pressure put upon Cuba to do so, however, as Obama's aspiration seems to be normalization at all costs. 

Nonetheless, Nova Korkus despairs that the prolonged conflict has changed the nature of the city itself.

His wife, Virginia, despairs that the mixed-race supporters of the National Party are disregarding their own history.

根据以上句子的句义，可以推知despair后接that从句时，despair的词义应为”绝望地认为/说..."。

既然despair可以后接that从句，就可以改为自由间接引语结构，即that从句作主句（去掉that），sb despairs或despaired作插入分句。例如：

His wife, Virginia, despairs that the mixed-race supporters of the National Party are disregarding their own history. 间接引语

The mixed-race supporters of the National Party are disregarding their own history, despairs his wife, Virginia. 自由间接引语

类似的用法如：

Tom says that Mary will come tomorrow. 间接引语

Mary will come tomorrow, says Tom. 自由间接引语

网友的这个句子就是自由间接引语结构，引语做了主句，引述分句以插入语的形式出现。

The eu has been “irrelevant” in the Syrian conflict, despairs one European diplomat. 自由间接引语结构。可以改为间接引语结构：

One European diplomat despairs that the eu has been "irrelevant” in the Syrian conflict.