williamandkateneagement460inset.jpgMario Testino

Mario Testino is finally dishing on some deets from the day he shot Will and Kate's royal engagement photo.

Testino, who was a fave photog of Will's late mom Princess Diana, said of the special few hours he spent with the royal couple in November:

    "You know, it's not so much what they say to each other because there is no time. Everything is compacted into a very short time because we have to produce these pictures. It's more like me screaming and trying to get everything to go. Well, not screaming, but getting in a fluster, I guess you say."

Testino added the duchess "looked fabulous" and he even helped do her own makeup.

We love Kate's down-to-earth approach to style!

The famed photog also revealed the relaxed portraits of the couple were taken with the help of specific music he used while photographing the late Princess Diana.

Find out which other famous celebs Mario has captured on film, and check out his more causal engagement shot of the royal pair, after the jump ...