20. In this Part—

“relevant parent” means, in relation to a qualifying person, the deceased relevant person, referred to in paragraph (b) of the definition of “qualifying person”;

“qualifying person” means a person—

(a) who has attained the age of 18 years, and

(b) whose mother or father or, as the case may be, adoptive mother or adoptive father—

(i) was a relevant person, and

(ii) is deceased.