After main clauses which contain adjectives like principal, seul, unique, premier, dernier, or any superlative, the subjunctive is optional - it depends on how concrete the speaker feels about what is being said.
Hélène est la seule personne qui puisse nous aider.
Hélène is the only person who can help us.
(Hélène may be the only person I think can help us, but there may be others.)
Hélène est la seule personne que je vois.
Hélène is the only person I see.
(No subjunctive, because I know this for a fact - I only see Hélène.)
C'est le meilleur livre que j'aie pu trouver.
That's the best book I could find.
(But it's not necessarily the best that exists.)
C'est le meilleur livre que j'ai écrit.
That's the best book I've written.
(I wrote three, and I know for a fact that this is the best one.)
Does ___ need the subjunctive? Find out with the Subjunctivator! | Subjunctive quiz




