NEW YORK (TheStreet) -- The pound sterling plunged from 1.50 to 1.32 per dollar in the hours following the results of U.K. referendum to leave the European Union, hitting a 30-year low.

CEO of Millennium Global Mark Astley believes that the dramatic response is slowing, but the pound will continue to lose more value over the next week.

"We've had the adjustment, we hit the air pocket. We had the 12% move on the day," Astley said on CNBC's "Power Lunch."

Before the vote yesterday Astley told CNBC's Michelle Caruso-Cabrera that the pound would go "way below last week's low of 1.40" and into the 1.30s if the referendum passed.

Astley believes that today's dive is an extremely rare event in the 45-year history of foreign exchange rates and "is going to be in the Hall of Fame of days in the foreign exchange market in terms of the aberration that we saw." Now, after the drop, it is "a marathon not a sprint," Astley added.

His currency outlook is that there will be another 5 to 15% decline in the rate of the pound per dollar, down into the 1.20s and possibly as low as 1.15. Astley's fund Millennium Global, which is a specialist currency and alternative investment firm with more than $16 billion under management, also foresees the euro rallying against the pound in the near future.