How to say "must be" in the sense of making an affirmative guess?

Question

Sorry if the question isn't clear enough. In English, we can make an affirmative guess based on prior information we received from someone/something by saying "X must be Y". Some example contexts below:

1. Manager at my job informs us that a new person will join the team and begin working here starting Monday morning. Sure enough, Monday morning comes, I see someone in the office I don't recognize and go "Oh, he must be the new person my manager was talking about".

2. Friend of mine told me about this really neat restaurant located on a certain road. Later, I'm driving on the same road and see a restaurant that matches my friend's description and go "This must be that restaurant my friend was talking about earlier".

I don't think the usual grammar pattern for must be (～なければならない・いけない and all its variants) works here, but if it does please let me know.

I've thought of some ways to express it below but not sure if they are even correct:

Example 1:

1. 彼は社長が話してた新人ですね
2. 彼は社長が話してた新人はずなんですね

Example 2:

1. これはさっき友達が話してたレストランだね。
2. これはさっき友達が話してたレストランはずなんだね

I don't know if "ね" or "はず" express this properly, or if I'm just wrong and there's a completely different way to express this.

Answer 1

You're correct that はず is the right word for this meaning of "must". However, you're using はず wrong. The correct grammar is noun + の + はず + だ/です. (はず behaves as a noun, and nouns should be joined with の.) Alternatively, you can just say ～でしょう, which is like "I suppose" but is enough in many cases.

• 彼は社長が言ってた新人のはずです。
  He must/should be the new recruit the president was talking about.
• これはさっき友達が言ってたレストランのはずです。
  This must/should be the restaurant my friend mentioned earlier.
• 空腹でしょう。
  You must be hungry.

You cannot use なければならない・いけない for this meaning. ね is like "huh?". Although it can be used with はずだ, you don't usually need it.