The Championship club announced the capture of the South Korean striker on Twitter:
Arsenal also confirmed on their official website that Park is off to the Championship:
Arsenal Football Club can confirm Ju Young Park has joined Championship side Watford on loan until the end of the 2013/14 season.
Park will be looking to gain first-team opportunities with The Hornets, while helping the team push for a possible promotion into the Premier League.
Everyone at Arsenal wishes Ju the best of luck for his time with Watford.
Many Gooners will likely react to this news with a mixture of surprise and apathy. The 28-year-old has done very little since arriving at Emirates Stadium in 2011. The biggest shock of this move is arguably the fact that Park is still on Arsenal's books at all.
He's appeared in a total of seven matches for the Gunners across all competitions. He spent the last season on loan at Celta Vigo, playing 21 matches and scoring three goals.
What's telling about Park's current standing with Arsene Wenger is that the Gunners are starving for strikers at the moment, and yet they felt that the better move would be to let him leave on a loan.
Even taking into account how disappointing he's been since arriving from Monaco, it's hard to argue that this loan doesn't benefit all parties involved.
Park gets a chance at regular first-team football in a competitive league; Arsenal found a way to offload one of their worst transfers of the past few years, at least temporarily; and Watford welcome in a striker who's had experience in both La Liga and Ligue 1.
While this is far from the most glamorous transfer on deadline day, it makes a lot of sense and could help propel the Hornets into the Premier League.