An overjoyed George Dryden told The Canadian Press on Friday that he was busy trying to arrange a trip with a testing company to the Saskatoon-based Diefenbaker Canada Centre.
"I'm greatly relieved," Dryden said. "We went from real disappointment to real joy."
Dryden said he planned to engage a Toronto-based company to do the DNA testing at the museum as soon as possible.
In a recent interview, the centre's executive director Michael Atkinson said he didn't believe the museum had any usable DNA that could help Dryden determine his paternity.
The museum was also concerned it couldn't be sure any particular DNA was in fact Diefenbaker's, Atkinson said.
A disappointed Dryden took that to be a refusal to allow testing.
However, in a letter this week, Atkinson says the museum has decided it will allow inspection and testing at Dryden's expense provided no damage to the artifacts occurs.
"Neither the curator nor I are DNA experts, and we respect your desire to have the items inspected by someone who has this expertise," Atkinson says in the letter to Dryden's lawyer.
"Such inspection must take place on our premises and under our supervision."
Dryden, 42, of Toronto, became aware last year of long-time family whispers that Canada's 13th prime minister, to whom he bears a strong resemblance, was his real father.
He also discovered in June that the man he had always believed to be his dad was not his biological parent.
His ailing mother, Mary Lou Dryden, a known confidante of Diefenbaker, then told him his father's name was John, but did not directly confirm having had an affair with the former prime minister.
Diefenbaker was not known to have had any children.
"If Diefenbaker does turn out to be my father, that's great, that's the end of the search," Dryden said.
"If it turns out that he's not, the next step is I've got to get through to my mom somehow and just say, 'Look, I've got to know who the hell my dad is because it's driving me a little bit batty.'"
Dryden said he didn't know where his mother was. He said he believes her husband was keeping her away from him.
Diefenbaker was Conservative prime minister from 1959 to 1963. He died in 1979.
Colin Perkel, The Canadian Press