His second name is Willem, after his grandfather.

他的中间名是威廉，取自他祖父的名字。

牛津词典

The second name in a binomen and in a trinomen [ Art . 5 ].

即一个二名式名称或三名式名称中的第二个名称 [ 第5条 ].

期刊摘选

Have you heard that your teeth are your second name card?

你有没有听说过,牙齿是人的第二张名片?

期刊摘选

He would never own to his second name.

他从不承认他的姓.

期刊摘选

His second name is Willem, after his grandfather.

他的中间名是威廉，取自他祖父的名字。

《牛津高阶英汉双解词典》