Correct: most/best/happy

[missionasker]

I wrote this sentence below and I was told there is something wrong with it:

They are the best happy couple that I have ever known

I wonder if it is OK to use "the best happy couple" here!? Pls help.

Thanks

 

[Anglika]

No. Comparatives are not formed with "best", which in itself is a superlative [good/better/best].

Either "They are the happiest couple" or "They are the most happy couple".