The 23-year-old Playboy heir popped the question to actress, whose appeared in "Falling Skies" and "Vampire Diaries", in London earlier this week, reported Us magazine.
Hugh's son had jetted overseas to Byrne's birthplace to ask her father for her hand in marriage prior to getting down on one knee with a massive yellow diamond.
After the 24-year-old "Harry Potter" actress said yes, the families celebrated their happy news.
Wearing a pink dress, the bride-to-be happily clutched her soon-to-be groom while celebrating at the Ritz hotel.
"Sending love and congratulations to my son Cooper and his fiancee Scarlett on their engagement!," Hugh posted on twitter.